The Sixth Amendment's Confrontation Clause guarantees a criminal defendant the right to confront the witnesses against him. The Clause bars the admission at trial of “testimonial statements” of an absent witness unless she is “unavailable to testify, and the defendant ha[s] had a prior opportunity” to cross-examine her. Crawford v. Washington, 541 U. S. 36, 53–54 (2004). And that prohibition applies in full to forensic evidence. So a prosecutor cannot introduce an absent laboratory analyst's testimonial out-of-court statements to prove the results of forensic testing. See Melendez- Diaz v. Massachusetts, 557 U. S. 305, 307, 329 (2009). The question presented here concerns the application of those principles to a case in which an expert witness restates an absent lab analyst's factual assertions to support his own opinion testimony. This Court has held that the Confrontation Clause's requirements apply only when the prosecution uses out-of-court statements for “the truth of the matter asserted.” Crawford, 541 U. S., at 60, n. 9. Some state courts, including the court below, have held that this condition is not met when an expert recites another analyst's statements as the basis for his opinion. Today, we reject that view. When an expert conveys an absent analyst's statements in support of his opinion, and the statements provide that support only if true, then the statements come into evidence for their truth. As this dispute illustrates, that will generally be the case when an expert relays an absent lab analyst's statements as part of offering his opinion. And if those statements are testimonial too—an issue we briefy address but do not resolve as to this case—the Confrontation Clause will bar their admission.
I
A
The Confrontation Clause provides that “[i]n all criminal prosecutions, the accused shall enjoy the right . . . to be confronted with the witnesses against him.” In operation, the Page Proof Pending Publication Clause protects a defendant's right of cross-examination by limiting the prosecution's ability to introduce statements made by people not in the courtroom. For a time, this Court held that the Clause's “preference for face-to-face” confrontation could give way if a court found that an out-of-court statement bore “adequate indicia of reliability.” Ohio v. Roberts, 448 U. S. 56, 65–66 (1980). But two decades ago, the Court changed course, to better refect original understandings. In Crawford v. Washington, the Court deemed it “fundamentally at odds with the right of confrontation” to admit statements based on judicial determinations of reliability. 541 U. S., at 61. The Clause, Crawford explained, “commands[ ] not that evidence be reliable, but that reliability be assessed in a particular manner: by testing in the crucible of cross-examination.” Ibid. And so the Clause bars the admission at trial of an absent witness's statements— however trustworthy a judge might think them—unless the witness is unavailable and the defendant had a prior chance to subject her to cross-examination.
But not always. The Clause's prohibition “applies only to testimonial hearsay”—and in that two-word phrase are two limits. Davis v. Washington, 547 U. S. 813, 823 (2006). First, in speaking about “witnesses”—or “those who bear testimony”—the Clause confnes itself to “testimonial statements,” a category whose contours we have variously described. Id., at 823, 826; see id., at 822 (statements “made in the course of police interrogation” were testimonial when “the primary purpose of the interrogation [was] to establish or prove past events potentially relevant to later criminal prosecution”); Michigan v. Bryant, 562 U. S. 344, 358, 359 (2011) (statements made to police “to meet an ongoing emergency” were “not procured with a primary purpose of creating an out-of-court substitute for trial testimony”); Melendez-Diaz, 557 U. S., at 311 (testimonial certifcates of the results of forensic analysis were created “under circumstances which would lead an objective witness reasonably to Page Proof Pending Publication Page Proof Pending Publication believe that the statement[s] would be available for use at a later trial”); infra, at 800. Second and more relevant here, the Clause bars only the introduction of hearsay—meaning, out-of-court statements offered “to prove the truth of the matter asserted.” Anderson v. United States, 417 U. S. 211, 219 (1974). When a statement is admitted for a reason unrelated to its truth, we have held, the Clause's “role in protecting the right of cross-examination” is not implicated. Ten nessee v. Street, 471 U. S. 409, 414 (1985); see Anderson, 417 U. S., at 220. That is because the need to test an absent witness ebbs when her truthfulness is not at issue. See ibid.; Street, 471 U. S., at 414; infra, at 795, 798.
Not long after Crawford, the Court made clear that the Confrontation Clause applies to forensic reports.
In Melendez-Diaz v. Massachusetts, state prosecutors introduced “certifcates of analysis” (essentially, affdavits) stating that lab tests had identifed a substance seized from the defendant as cocaine. 557 U. S., at 308. But the State did not call as witnesses the analysts who had conducted the tests and signed the certifcates. We held that a “straightforward application” of Crawford showed a constitutional violation. 557 U. S., at 312. The certifcates were testimonial: They had an “evidentiary purpose,” identical to the one served had the analysts given “live, in-court testimony.” Id., at 311. And the certifcates were offered to prove the truth of what they asserted: that the seized powder was in fact cocaine. See id., at 310–311. So the defendant had a right to cross- examine the lab-analyst certifers. In reaching that conclusion, we rejected the State's claim that the results of so- called “neutral, scientifc testing” should be subject to a different rule. Id., at 317. We again underscored that the Confrontation Clause commanded not reliability but one way of testing it—through cross-examination. See ibid. And we thought that method might have plenty to do in cases involving forensic analysis. After all, lab tests are “not uniquely immune from the risk of manipulation” or mistake. Id., at 318. The defendant might have used cross- examination to probe “what tests the analysts performed,” whether those tests “present[ed] a risk of error, ” and whether the analysts had the right skill set to “interpret[ ] their results.” Id., at 320.
Two years later, the Court relied on Melendez-Diaz to hold that a State could not introduce one lab analyst's written fndings through the testimony of another. In Bullcoming v. New Mexico, 564 U. S. 647, 651–652 (2011), an analyst tested the blood-alcohol level of someone charged with drunk driving, and prepared a “testimonial certifcation” reporting that the level was higher than legal. But by the time the driver's trial began, that analyst had been placed on unpaid leave. So the State instead called a different analyst from the same lab to testify as to what the certifcation said. The substitute analyst had similar qualifcations, and knew about the type of test performed. But the Court held that insuffcient to satisfy the Confrontation Clause. The “surrogate testimony,” the Court explained, “could not convey what [the certifying analyst] knew or observed” about “the particular test and testing process he employed.” Id., at 661. Nor could that “testimony expose any lapses or lies on the certifying analyst's part,” or offer any insight into whether his leave-without-pay was the result of misconduct. Id., at 662. Concluded the Court: “[W]hen the State elected to introduce [the] certifcation,” its author—and not any substitute—“became [the] witness [that the defendant] had the right to confront.” Id., at 663.
The very next Term brought another case in which one lab analyst related what another had found—though this time on the way to stating her own conclusion. In Williams v. Illi nois, 567 U. S. 50 (2012), state police sent vaginal swabs from a rape victim known as L. J. to a private lab for DNA testing. When the lab sent back a DNA profle, a state analyst checked it against the police department's database and found that it matched the profle of prior arrestee Sandy WilPage Proof Pending Publication liams. The State charged Williams with the rape, and he went to trial. The prosecution chose not to bring the private lab analyst to the stand. Instead, it called Sandra Lambatos, the state analyst who had searched the police database and found the DNA match. Lambatos had no frsthand knowledge of how the private lab had produced its results; she did not even know whether those results actually came from L. J.'s vaginal swabs (as opposed to some other sample). But she spoke repeatedly about comparing Williams's DNA to the DNA “found in [L. J.'s] vaginal swabs.” Id., at 61, 71 (plurality opinion); see id., at 124 (Kagan, J., dissenting). So in addition to describing how she discovered a match, Lambatos became the conduit for what a different analyst had reported—that a particular DNA profle came from L. J.'s vaginal swabs. Williams objected, at trial and later: He thought that, just as in Bullcoming, crucial evidence had been admitted through a surrogate expert, thus violating his right of confrontation.
But the Illinois Supreme Court rejected Williams's claim, holding that Lambatos's testimony about the private lab analyst's fnding did not raise a Confrontation Clause issue. See People v. Williams, 238 Ill. 2d 125, 143–144, 939 N. E. 2d 268, 278–279 (2010). The court explained that under state evidence law, an expert can disclose “underlying facts and data” for “the purpose of explaining the basis for [her] opinion.” Id., at 137, 143, 939 N. E. 2d, at 274–275, 278. And when she does so, the court held, the testimony is not subject to the Confrontation Clause because it is not admitted “for the truth of the matter asserted.” Id., at 143, 939 N. E. 2d, at 278. Thus, Lambatos could relay the private lab's fnding that L. J.'s vaginal swabs produced a certain DNA profle in order to “explain[] the basis for her opinion” that “there was a DNA match between [Williams's] blood sample and the semen sample recovered from L. J.” Id., at 150, 939 N. E. 2d, at 282. The admission of the private lab report's contents for that “limited purpose,” the court reasoned, would Page Proof Pending Publication “aid the [factfnder] in assessing the value of [Lambatos's] opinion.” Id., at 144, 939 N. E. 2d, at 278; see id., at 150, 939 N. E. 2d, at 282.
This Court granted Williams's petition for certiorari, but failed to produce a majority opinion. Four Members of the Court approved the Illinois Supreme Court's approach to “basis evidence,” and agreed that Lambatos's recitation of the private lab's fndings served “the legitimate nonhearsay purpose of illuminating the expert's thought process.” Wil liams, 567 U. S., at 78 (plurality opinion). But the remaining fve Members rejected that view. Those fve stated, in two opinions, that basis evidence is generally introduced for its truth, and was so introduced at Williams's trial. Justice Thomas explained that “the purportedly limited reason for [the basis] testimony—to aid the factfnder in evaluating the expert's opinion—necessarily entail[ed] an evaluation of whether [that] testimony [was] true”: “[T]he validity of Lambatos'[s] opinion ultimately turned on the truth of [the private lab analyst's] statements.” Id., at 106, n. 1, 108 (opinion concurring in judgment). A dissent for another four Justices agreed: “[T]he utility of the [private analyst's] statement that Lambatos repeated logically depended on its truth.” Id., at 132 (opinion of Kagan, J.). And the State could not avoid that conclusion by “rely[ing] on [Lambatos's] status as an expert.” Id., at 126. Those shared views might have made for a happy majority, except that a different Confrontation Clause issue intruded. Justice Thomas thought that the private lab report was not testimonial because it lacked suffcient formality, so affrmed the Illinois Supreme Court on that alternative ground. The bottom line was that Williams lost, even though fve Members of this Court rejected the state court's “not for the truth” reasoning.1 1The Court also failed to reach agreement on the testimonial issue. The four Justices who accepted the state court's “not for the truth” view also concluded that the report was not testimonial. See Williams, 567 U. S., at 81–86 (plurality opinion). But they did so for reasons different Page Proof Pending Publication Our opinions in Williams “have sown confusion in courts across the country” about the Confrontation Clause's application to expert opinion testimony. Stuart v. Alabama, 586 U. S. 1026, 1027 (2018) (Gorsuch, J., dissenting from denial of certiorari). Some courts have applied the Williams plurality's “not for the truth” reasoning to basis testimony, while others have adopted the opposed fve-Justice view.2 This case emerged out of that muddle.
B
Like Melendez-Diaz, this case involves drugs. In December 2019, Arizona law enforcement offcers executed a search warrant on a property in the foothills of Yuma County. Inside a shed on the property, they found petitioner Jason Smith. They also found a large quantity of what appeared to be drugs and drug-related items. As a result, Smith was charged with possessing dangerous drugs (methamphetamine) for sale; possessing marijuana for sale; possessing narcotic drugs (cannabis) for sale; and possessing drug paraphernalia. He pleaded not guilty, and the case was set for trial.
In preparation, the State sent items seized from the shed to a crime lab run by the Arizona Department of Public Safety (DPS) for a “full scientifc analysis.” App. to Pet. from Justice Thomas's. Compare ibid. with id., at 110–117 (opinion concurring in judgment). The result was that no single rationale for affrmance garnered a majority.
2Compare, e. g., State v. Mercier, 2014 ME 28, ¶¶12–14, 87 A. 3d 700, 704 (accepting the “not for the truth” rationale for admitting an expert's basis testimony); State v. Hutchison, 482 S. W. 3d 893, 914 (Tenn. 2016); United States v. Murray, 540 Fed. Appx. 918, 921 (CA11 2013), with People v. Sanchez, 63 Cal. 4th 665, 684, 374 P. 3d 320, 333 (2016) (rejecting the “not for the truth” rationale for admitting an expert's basis testimony); Martin v. State, 60 A. 3d 1100, 1107 (Del. 2013); Young v. United States, 63 A. 3d 1033, 1045 (D. C. 2013); Leidig v. State, 475 Md. 181, 234, n. 23, 256 A. 3d 870, 901, n. 23 (2021); Commonwealth v. Jones, 472 Mass. 707, 714, 37 N. E. 3d 589, 597 (2015).
Page Proof Pending Publication for Cert. 127a. The State's request identifed Smith as the individual “associated” with the substances, listed the charges against him, and noted that “[t]rial ha[d] been set.” Ibid. Analyst Elizabeth Rast communicated with prosecutors about exactly which items needed to be examined, and then ran the requested tests. See id., at 99a.
Rast prepared a set of typed notes and a signed report, both on DPS letterhead, about the testing. The notes documented her lab work and results. They disclosed, for each of eight items: a “[d]escription” of the item; the weight of the item and how the weight was measured; the test(s) she performed on the item, including whether she frst ran a “[b]lank” on the testing equipment; the results of those tests; and a “[c]onclusion” about the item's identity. See id., at 88a–98a. The signed report then distilled the notes into two pages of ultimate fndings, denoted “results/interpretations.” See id., at 85a–87a. After listing the eight items, the report stated that four “[c]ontained a usable quantity of methamphetamine,” three “[c]ontained a usable quantity of marijuana,” and one “[c]ontained a usable quantity of cannabis.” Id., at 86a–87a. The State originally planned for Rast to testify about those matters at Smith's trial.
But with three weeks to go, the State called an audible, replacing Rast with a different DPS analyst as its expert witness. In the time between testing and trial, Rast had stopped working at the lab, for unexplained reasons. And the State chose not to rely on the now-former employee as a witness. So the prosecutors fled an amendment to their “fnal pre-trial conference statement” striking out the name Elizabeth Rast and adding “Greggory Longoni, forensic scientist (substitute expert).” Id., at 26a. Longoni had no prior connection to the Smith case, and the State did not claim otherwise.
Its amendment simply stated that “Mr. Longoni will provide an independent opinion on the drug testing performed by Elizabeth Rast.” Ibid. And it continued: “Ms. Rast will not be called. [Mr. Longoni] is expected to have the same conclusion.” Ibid. Page Proof Pending Publication And he did come to the same conclusion, in reliance on Rast's records. Because he had not participated in the Smith case, Longoni prepared for trial by reviewing Rast's report and notes. And when Longoni took the stand, he referred to those materials and related what was in them, item by item by item. As to each, he described the specifc “scientifc method[s]” Rast had used to analyze the substance (e. g., a microscopic examination, a chemical color test, a gas chromatograph/mass spectrometer test). Id., at 41a; see id., at 42a, 46a–48a. And as to each, he stated that the testing had adhered to “general principles of chemistry,” as well as to the lab's “policies and practices,” id., at 47a–48a; see id., at 40a; so he noted, for example, that Rast had run a “blank” to confrm that testing equipment was not contaminated, id., at 42a, 47a. After thus telling the jury what Rast's records conveyed about her testing of the items, Longoni offered an “independent opinion” of their identity. Id., at 46a–47a, 49a. More specifcally, the opinions he offered were: that Item 26 was “a usable quantity of marijuana,” that Items 20A and 20B were “usable quantit[ies] of methamphetamine,” and that Item 28 was “[a] usable quantity of cannabis.” Ibid. After Smith was convicted, he brought an appeal focusing on Longoni's testimony. In Smith's view, the State's use of a “substitute expert”—who had not participated in any of the relevant testing—violated his Confrontation Clause rights. Id., at 26a; see Brief for Appellant Smith in No. 1 CA–CR 21– 0451 (Ariz. Ct. App.), pp. 20–23.
The real witness against him, Smith urged, was Rast, through her written statements; but he had not had the opportunity to cross- examine her. See ibid. The State disagreed. In its view, Longoni testifed about “his own independent opinions,” even though making use of Rast's records. Brief for Appellee Arizona in No. 1 CA–CR 21–0451 (Ariz. Ct. App.), p. 22. So Longoni was the only witness Smith had a right to confront. See ibid.
The Arizona Court of Appeals affrmed Smith's convictions, rejecting his Confrontation Clause challenge. It rePage Proof Pending Publication lied on Arizona precedent (similar to the Illinois Supreme Court's decision in Williams) stating that an expert may testify to “the substance of a non-testifying expert's analysis, if such evidence forms the basis of the [testifying] expert's opinion.” App. to Pet. for Cert. 11a–12a (quoting State ex rel. Montgomery v. Karp, 236 Ariz. 120, 124, 336 P. 3d 753, 757 (App. 2014)). That is because, the Arizona courts have said, the “underlying facts” are then “used only to show the basis of [the in-court witness's] opinion and not to prove their truth.” Ibid., 336 P. 3d, at 757. On that view, the Court of Appeals held, Longoni could constitutionally “present[ ] his independent expert opinions” as “based on his review of Rast's work.” App. to Pet. for Cert. 11a.
We granted certiorari to consider that reasoning, 600 U. S. ––– (2023), and we now reject it.3
II
Smith's confrontation claim can succeed only if Rast's statements came into evidence for their truth. As earlier explained, the Clause applies solely to “testimonial hearsay.” Davis, 547 U. S., at 823 (emphasis added); see supra, at 784. 3The question on which we granted certiorari made reference as well to another aspect of the Court of Appeals' reasoning. That question asks whether the Confrontation Clause permits “testimony by a substitute expert conveying the testimonial statements of a nontestifying forensic analyst, on the grounds that (a) the testifying expert offers some independent opinion and the analyst's statements are offered not for their truth but to explain the expert's opinion, and (b) the defendant did not independently seek to subpoena the analyst.” Pet. for Cert. i. The “(b)” in that question arises from the following sentence in the court's opinion: “Had Smith sought to challenge Rast's analysis, he could have called her to the stand and questioned her, but he chose not to do so.” App. to Pet. for Cert. 12a. We need not spend much time on that rationale because the State rightly does not defend it. As we held in Melendez-Diaz, a defendant's “ability to subpoena” an absent analyst “is no substitute for the right of confrontation.” 557 U. S., at 324. The Confrontation Clause “imposes a burden on the prosecution to present its witnesses, not on the defendant to bring those adverse witnesses into court.” Ibid. Page Proof Pending Publication And that means the Clause “does not bar the use of testimonial statements for purposes other than establishing the truth of the matter asserted.” Crawford, 541 U. S., at 60, n. 9. So a court analyzing a confrontation claim must identify the role that a given out-of-court statement—here, Rast's statements about her lab work—served at trial. On that much, indeed, the entire Williams Court agreed. Amid all the fracturing that case produced, every Justice defned its primary question in the same way: whether the absent analyst's statements were introduced for their truth. See 567 U. S., at 57–58 (plurality opinion); id., at 104 (Thomas, J., concurring in judgment); id., at 125–126 (Kagan, J., dissenting). The parties here likewise concur in that framing. See Brief for Smith 28–29; Brief for Arizona 17–18. If Rast's statements came in to establish the truth of what she said, then the Clause's alarms begin to ring; but if her statements came in for another purpose, then those alarms fall quiet. Where the parties disagree, of course, is in answering that purpose question. Smith argues that the “for the truth” condition is satisfed here, just as much as in Melendez-Diaz or Bullcoming. See Brief for Smith 23–28; supra, at 785– 786. In his view, Rast's statements were conveyed, via Longoni's testimony, to establish that what she said happened in the lab did in fact happen. Or put more specifcally, those statements were conveyed to show that she used certain standard procedures to run certain tests, which enabled identifcation of the seized items. The State sees the matter differently. See Brief for Arizona 19–26. Echoing the Arizona Court of Appeals (and the Illinois Supreme Court in Williams), the State argues that Rast's statements came into evidence not for their truth, but instead to “show the basis” of the in-court expert's independent opinion. Brief for Arizona 21; see supra, at 787–788. And to defend that characterization, Arizona emphasizes that its Rule of Evidence 703 (again, like Illinois's) authorizes the admission of such statements only for that purpose—i. e., to “help[ ] the Page Proof Pending Publication jury [to] evaluate” the opinion testimony. Brief for Arizona 20–21; see post, at 814 (Alito, J., concurring in judgment) (arguing the same as to Federal Rule of Evidence 703). Evidentiary rules, though, do not control the inquiry into whether a statement is admitted for its truth. That inquiry, as just described, marks the scope of a federal constitutional right. See supra, at 792–793. And federal constitutional rights are not typically defned—expanded or contracted— by reference to non-constitutional bodies of law like evidence rules.4 The confrontation right is no different, as Crawford made clear. “Where testimonial statements are involved,” that Court explained, “the Framers [did not mean] to leave the Sixth Amendment's protection to the vagaries of the rules of evidence.” 541 U. S., at 61. Justice Thomas reiterated the point in Williams: “[C]oncepts central to the application of the Confrontation Clause are ultimately matters of federal constitutional law that are not dictated by state or federal evidentiary rules.” 567 U. S., at 105 (opinion concurring in judgment). We therefore do not “accept [a State's] nonhearsay label at face value.” Id., at 106; see id., at 132 (Kagan, J., dissenting). Instead, we conduct an independent analysis of whether an out-of-court statement was admitted for its truth, and therefore may have compromised a defendant's right of confrontation.
We did just that in Tennessee v. Street—and in so doing showcased how an out-of-court statement can come into evidence for a non-truth-related reason. See 471 U. S., at 410– 417. Street was charged with murder, based mostly on a 4One qualifcation is appropriate. If an evidentiary rule refects a long- established understanding, then it might shed light on the historical meaning of the Confrontation Clause. But that could not possibly be said of Rule 703—the rule Arizona cites to support the introduction of basis evidence. On the contrary, that rule is a product of the late-20th century, and was understood from the start to depart from past practice. See Brief for Richard D. Friedman as Amicus Curiae 17; Advisory Commit- tee's Notes on Fed. Rule Evid. 703, 28 U. S. C. App., p. 393. Page Proof Pending Publication stationhouse confession. At trial, he claimed that the confession was coerced, and in a peculiar way: The sheriff, he said, had read aloud an accomplice's confession and forced him to repeat it. On rebuttal, the State introduced the other confession (through the sheriff's testimony) to demonstrate to the jury all the ways its content deviated from Street's. We upheld that use as “nonhearsay.” Id., at 413. The other confession came in, we explained, not to prove “the truth of [the accomplice's] assertions” about how the murder happened, but only to disprove Street's claim about how the sheriff elicited his own confession. Ibid. Or otherwise said, the point was to show, by highlighting the two confessions' differences, that Street's was not a “coerced imitation.” Id., at 414. For that purpose, the truth of the accomplice's confession (and the credibility of the accomplice himself) was irrelevant.
But truth is everything when it comes to the kind of basis testimony presented here. If an expert for the prosecution conveys an out-of-court statement in support of his opinion, and the statement supports that opinion only if true, then the statement has been offered for the truth of what it asserts. How could it be otherwise? “The whole point” of the prosecutor's eliciting such a statement is “to establish— because of the [statement's] truth—a basis for the jury to credit the testifying expert's” opinion. Stuart, 586 U. S., at 1028 (Gorsuch, J., dissenting from denial of certiorari) (emphasis in original). Or said a bit differently, the truth of the basis testimony is what makes it useful to the prosecutor; that is what supplies the predicate for—and thus gives value to—the state expert's opinion. So “[t]here is no meaningful distinction between disclosing an out-of-court statement” to “explain the basis of an expert's opinion” and “disclosing that statement for its truth.” Williams, 567 U. S., at 106 (Thomas, J., concurring in judgment). A State may use only the former label, but in all respects the two purposes merge.
Page Proof Pending Publication Page Proof Pending Publication Or to see the point another way, consider it from the factfnder's perspective. In the view of the Arizona courts, an expert's conveyance of another analyst's report enables the factfnder to “determine whether [the expert's] opinion should be found credible.” Karp, 236 Ariz., at 124, 336 P. 3d, at 757; see Williams, 238 Ill. 2d, at 144, 939 N. E. 2d, at 278 (also stating that such a report “aid[s] the jury in assessing the value of [the expert's] opinion”); supra, at 787–788, 792. That is no doubt right. The jury cannot decide whether the expert's opinion is credible without evaluating the truth of the factual assertions on which it is based. See D. Kaye, D. Bernstein, A. Ferguson, M. Wittlin, & J. Mnookin, The New Wigmore: Expert Evidence § 5.4.1, p. 271 (3d ed. 2021). If believed true, that basis evidence will lead the jury to credit the opinion; if believed false, it will do the opposite. See Williams, 567 U. S., at 106, and n. 1 (Thomas, J., concurring in judgment); id., at 126–127 (Kagan, J., dissenting). But that very fact is what raises the Confrontation Clause problem. For the defendant has no opportunity to challenge the veracity of the out-of-court assertions that are doing much of the work.
And if that explanation seems a bit abstract, then take this case as its almost-too-perfect illustration. Recall that Rast tested eight seized items before she disappeared from the scene. At trial, the prosecutor asked the State's “substitute expert” Longoni to testify about four of them (with the rest dropping out of the case). App. to Pet. for Cert. 26a. A recap of their exchange about one item will be enough; the rest followed the same pattern. Remember as you read that Longoni, though familiar with the lab's general practices, had no personal knowledge about Rast's testing of the seized items. Rather, as his testimony makes clear, what he knew on that score came only from reviewing Rast's records. With that as background: Q Turn your attention to Item 26. I'm going to hand you what's been marked as State's Exhibit 98 [Rast's notes]. . . . Did you review how [Item] 26 was tested in this case?
A Yes.
Q When you reviewed it, did you notice whether the [standard lab] policies and practices that you have just described were followed?
A Yes.
Q Were they followed?
A Yes.
.
.
.
.
.
Q From your review of the lab notes in this case, can you tell me what scientifc method was used to analyze Item 26?
A Yes.
Q And what was used?
A The microscopic examination and the chemical color test. . . .
Q That was done in this case?
A Yes, it was.
Q Was there a blank done to prevent contamination, make sure everything was clean?
A According to the notes, yes.
.
.
.
.
.
Q In reviewing what was done, your knowledge and training as a forensic scientist, your knowledge and experience with DPS's policies, practices, procedures, your knowledge of chemistry, the lab notes, the intake records, the chemicals used, the tests done, can you form an independent opinion on the identity of Item 26?
A Yes.
Q What is that opinion?
A That is a usable quantity of marijuana.
Id., at 39a–42a, 46a. And then the prosecutor went on to Items 20A, 20B, and 28, asking similar questions, receiving similar answers based on Rast's records, and fnally eliciting similar “independent opinions”—which were no more than Page Proof Pending Publication Page Proof Pending Publication what Rast herself had concluded. See supra, at 790–791. “Yes,” Longoni confrmed, just as Item 26 was a “usable quantity of marijuana,” Items 20A and 20B were “usable quantit[ies] of methamphetamine” and Item 28 was a “usable quantity of cannabis.” App. to Pet. for Cert. 46a, 47a, 49a. Rast's statements thus came in for their truth, and no less because they were admitted to show the basis of Longoni's expert opinions. All those opinions were predicated on the truth of Rast's factual statements. Longoni could opine that the tested substances were marijuana, methamphetamine, and cannabis only because he accepted the truth of what Rast had reported about her work in the lab—that she had performed certain tests according to certain protocols and gotten certain results. And likewise, the jury could credit Longoni's opinions identifying the substances only because it too accepted the truth of what Rast reported about her lab work (as conveyed by Longoni). If Rast had lied about all those matters, Longoni's expert opinion would have counted for nothing, and the jury would have been in no position to convict. So the State's basis evidence—more precisely, the truth of the statements on which its expert relied—propped up its whole case. But the maker of those statements was not in the courtroom, and Smith could not ask her any questions.
Approving that practice would make our decisions in Melendez-Diaz and Bullcoming a dead letter, and allow for easy evasion of the Confrontation Clause. As earlier described, those two decisions applied Crawford in “straightforward” fashion to forensic evidence. Melendez-Diaz, 557 U. S., at 312; see Bullcoming, 564 U. S., at 659–661; supra, at 785–786. The frst prevented the introduction of a lab analyst's testimonial report sans lab analyst. The second refused to accede to the idea that any old analyst—i. e., a substitute who had not taken part in the lab work—would do. Arizona offers only a slight variation. On its view, a surrogate analyst can testify to all the same substance—that is, someone Page Proof Pending Publication else's substance—as long as he bases an “independent opinion” on that material. And that is true even if, as here, the proffered opinion merely replicates, rather than somehow builds on, the testing analyst's conclusions. So every testimonial lab report could come into evidence through any trained surrogate, however remote from the case. And no defendant would have a right to cross-examine the testing analyst about what she did and how she did it and whether her results should be trusted. In short, Arizona wants to end run all we have held the Confrontation Clause to require. It cannot.
Properly understood, the Clause still allows forensic experts like Longoni to play a useful role in criminal trials. Because Longoni worked in the same lab as Rast, he could testify from personal knowledge about how that lab typically functioned—the standards, practices, and procedures it used to test seized substances, as well as the way it maintained chains of custody. (Indeed, Longoni did just that in a different part of his testimony. See App. to Pet. for Cert. 32a– 39a.) Or had he not been familiar with Rast's lab, he could have testifed in general terms about forensic guidelines and techniques—perhaps explaining what it means for a lab to be accredited and what requirements accreditation imposes. Or as the Williams plurality and dissent both observed, he might have been asked—and could have answered—any number of hypothetical questions, taking the form of: “If or assuming some out-of-court statement were true, what would follow from it?” See 567 U. S., at 67–68; id., at 129, n. 2. (The State of course would then have to separately prove the thing assumed.) The United States, appearing as amicus curiae in support of neither party, usefully addressed these matters at oral argument, distinguishing Longoni's testimony as block-quoted above from the various kinds of testimony just described. See Tr. of Oral Arg. 36– 41. The latter forms of testimony allow forensic expertise to inform a criminal case without violating the defendant's right of confrontation. And we offer these merely as examples; there may be others.
But as the United States acknowledged, the bulk of Longoni's testimony took no such permissible form. Ibid. Here, the State used Longoni to relay what Rast wrote down about how she identifed the seized substances. Longoni thus effectively became Rast's mouthpiece. He testifed to the precautions (she said) she took, the standards (she said) she followed, the tests (she said) she performed, and the results (she said) she obtained. The State offered up that evidence so the jury would believe it—in other words, for its truth. So if the out-of-court statements were also testimonial, their admission violated the Confrontation Clause. Smith would then have had a right to confront the person who actually did the lab work, not a surrogate merely reading from her records.
III
What remains is whether the out-of-court statements Longoni conveyed were testimonial. As earlier explained, that question is independent of everything said above: To implicate the Confrontation Clause, a statement must be hearsay (“for the truth”) and it must be testimonial—and those two issues are separate from each other. See supra, at 784–785. The latter, this Court has stated, focuses on the “primary purpose” of the statement, and in particular on how it relates to a future criminal proceeding. See ibid. (noting varied formulations of the standard).5 A court must therefore identify the out-of-court statement introduced, and must de5Given that focus, the mine-run of materials on which most expert witnesses rely in forming opinions—including books and journals, surveys, and economic or scientifc studies—will raise no serious confrontation issues. See Brief for United States as Amicus Curiae 13–17 (giving examples of classic expert-basis evidence). That is because the preparation of those materials generally lacks any “evidentiary purpose.” Melendez- Diaz, 557 U. S., at 311.
Page Proof Pending Publication termine, given all the “relevant circumstances,” the principal reason it was made. Bryant, 562 U. S., at 369.
But that issue is not now ft for our resolution. The question presented in Smith's petition for certiorari did not ask whether Rast's out-of-court statements were testimonial. See supra, at 792, n. 3 (quoting Pet. for Cert. i). Instead, it took as a given that they were. See id., at i. That presentation refected the Arizona Court of Appeals' opinion. As described earlier, that court relied on the “not for the truth” rationale we have just rejected. See supra, at 791–792. It did not decide whether Rast's statements were testimonial. Nor, to our knowledge, did the trial court ever take a stance on that issue. Because “we are a court of review, not of frst view,” we will not be the pioneer court to decide the matter. Cutter v. Wilkinson, 544 U. S. 709, 718, n. 7 (2005). And indeed, we are not sure if there remains a matter to decide. Smith argues that the State has forfeited the argument: Arizona, he says, “gave no hint in the proceedings below that it believed Rast's statements were anything but testimonial.” Reply Brief 3. The State denies that assertion, pointing to a passage about Williams in its lower court briefng. See Brief for Arizona 39, n. 14. The dispute is best addressed by a state court. So we return the testimonial issue, including the threshold forfeiture matter, to the Arizona Court of Appeals.
But we offer a few thoughts, based on the arguments made here, about the questions the state court might usefully address if the testimonial issue remains live. First, the court will need to consider exactly which of Rast's statements are at issue. In this Court, the parties disputed whether Longoni was reciting from Rast's notes alone, or from both her notes and fnal report. See supra, at 790 (describing those documents). In Arizona's view, everything Longoni testifed to came from Rast's notes; although he at times used the word “report,” a close comparison of the documents and his Page Proof Pending Publication testimony reveals (the State says) that he meant only the notes. See Brief for Arizona 39–40; Tr. of Oral Arg. 69–72; see also App. to Pet. for Cert. 39a–40a, 48a. Smith disagrees, taking Longoni's references to the “report,” as well as the notes, at face value. According to Smith, Longoni “relied on both” documents and in fact “treated them as a unit,” with the notes “attached” to the report as “essentially an appendix.” Reply Brief 4; Tr. of Oral Arg. 25, 98. Resolving that dispute might, or then again might not, affect the court's ultimate disposition of Smith's Confrontation Clause claim. We note only that before the court can decide the primary purpose of the out-of-court statements introduced at Smith's trial, it needs to determine exactly what those statements were.
In then addressing the statements' primary purpose—why Rast created the report or notes—the court should consider the range of recordkeeping activities that lab analysts engage in. See generally supra, at 784–785 (describing formulations of the testimonial inquiry). After all, some records of lab analysts will not have an evidentiary purpose. The United States as amicus curiae notes, for example, that lab records may come into being primarily to comply with laboratory accreditation requirements or to facilitate internal review and quality control. See Tr. of Oral Arg. 51. Or some analysts' notes may be written simply as reminders to self. See id., at 20, 52. In those cases, the record would not count as testimonial. To do so, the document's primary purpose must have “a focus on court.” Id., at 52. And again, the state court on remand should make that assessment as to each record whose substance Longoni conveyed.
IV
Our holding today follows from all this Court has held about the Confrontation Clause's application to forensic evidence. A State may not introduce the testimonial out-ofcourt statements of a forensic analyst at trial, unless she is Page Proof Pending Publication unavailable and the defendant has had a prior chance to cross-examine her.
See Crawford, 541 U. S., at 68; Melendez-Diaz, 557 U. S., at 311. Neither may the State introduce those statements through a surrogate analyst who did not participate in their creation. See Bullcoming, 564 U. S., at 663. And nothing changes if the surrogate—as in this case—presents the out-of-court statements as the basis for his expert opinion. Those statements, as we have explained, come into evidence for their truth—because only if true can they provide a reason to credit the substitute expert. So a defendant has the right to cross-examine the person who made them.
That means Arizona does not escape the Confrontation Clause just because Rast's records came in to explain the basis of Longoni's opinion. The Arizona Court of Appeals thought otherwise, and so we vacate its judgment. To address the additional issue of whether Rast's records were testimonial (including whether that issue was forfeited), we remand the case for further proceedings not inconsistent with this opinion.
It is so ordered.