Petitioners, two minor children and their parents, alleged in their suit against respondent that the childrens serious birth defects had been caused by the mothers prenatal ingestion of Bendectin, a prescription drug marketed by respondent. The District Court granted respondent summary judgment based on a well-credentialed experts affidavit concluding, upon reviewing the extensive published scientific literature on the subject, that maternal use of Bendectin has not been shown to be a risk factor for human birth defects. Although petitioners had responded with the testimony of eight other well-credentialed experts, who based their conclusion that Bendectin can cause birth defects on animal studies, chemical structure analyses, and the unpublished "reanalysis" of previously published human statistical studies, the court determined that this evidence did not meet the applicable "general acceptance" standard for the admission of expert testimony. The Court of Appeals agreed and affirmed, citing Frye v. United States, 54 App. D.C. 46, 47, 293 F. 1013, 1014, for the rule that expert opinion based on a scientific technique is inadmissible unless the technique is "generally accepted" as reliable in the relevant scientific community.

Held:

The Federal Rules of Evidence, not Frye, provide the standard for admitting expert scientific testimony in a federal trial. Pp. 4-17.

(a) Fryes "general acceptance" test was superseded by the Rules adoption. The Rules occupy the field, United States v. Abel, 469 U.S. 45, 49, and, although the common law of evidence may serve as an aid to their application, id., at 51-52, respondents assertion that they somehow assimilated Frye is unconvincing. Nothing in the Rules as a [509 U.S. 579, 2] whole or in the text and drafting history of Rule 702, which specifically governs expert testimony, gives any indication that "general acceptance" is a necessary precondition to the admissibility of scientific evidence. Moreover, such a rigid standard would be at odds with the Rules liberal thrust and their general approach of relaxing the traditional barriers to "opinion" testimony. Pp. 4-8.

(b) The Rules - especially Rule 702 - place appropriate limits on the admissibility of purportedly scientific evidence by assigning to the trial judge the task of ensuring that an experts testimony both rests on a reliable foundation and is relevant to the task at hand. The reliability standard is established by Rule 702s requirement that an experts testimony pertain to "scientific . . . knowledge," since the adjective "scientific" implies a grounding in sciences methods and procedures, while the word "knowledge" connotes a body of known facts or of ideas inferred from such facts or accepted as true on good grounds. The Rules requirement that the testimony "assist the trier of fact to understand the evidence or to determine a fact in issue" goes primarily to relevance by demanding a valid scientific connection to the pertinent inquiry as a precondition to admissibility. Pp. 9-12.

(c) Faced with a proffer of expert scientific testimony under Rule 702, the trial judge, pursuant to Rule 104(a), must make a preliminary assessment of whether the testimonys underlying reasoning or methodology is scientifically valid and properly can be applied to the facts at issue. Many considerations will bear on the inquiry, including whether the theory or technique in question can be (and has been) tested, whether it has been subjected to peer review and publication, its known or potential error rate and the existence and maintenance of standards controlling its operation, and whether it has attracted widespread acceptance within a relevant scientific community. The inquiry is a flexible one, and its focus must be solely on principles and methodology, not on the conclusions that they generate.