-In principle, under the Federal Rules no common law of evidence
remains.  `All relevant evidence is admissible, except as otherwise
provided . . . .'  In reality, of course, the body of common law
knowledge continues to exist, though in the somewhat altered form of a
source of guidance in the exercise of delegated powers.-  Id., at 51-
52.  We found the common-law precept at issue in the Abel case
entirely consistent with Rule 402's general requirement of
admissibility, and considered it unlikely that the drafters had
intended to change the rule.  Id., at 50-51. In Bourjaily v. United
States, 483 U. S. 171 (1987), on the other hand, the Court was unable
to find a particular common-law doctrine in the Rules, and so held it
superseded.
  Here there is a specific Rule that speaks to the contested issue.
Rule 702, governing expert testimony, provides:
      -If scientific, technical, or other specialized knowledge will
assist the trier of fact to understand the evidence or to determine a
fact in issue, a witness qualified as an expert by knowledge, skill,
experience, training, or education, may testify thereto in the form of
an opinion or otherwise.-  Nothing in the text of this Rule
establishes -general acceptance- as an absolute prerequisite to
admissibility. Nor does respondent present any clear indication that
Rule 702 or the Rules as a whole were intended to incorporate a -
general acceptance- standard.  The drafting history makes no mention
of Frye, and a rigid -general acceptance- requirement would be at odds
with the -liberal thrust-of the Federal Rules and their -general
approach of relaxing the traditional barriers to `opinion' testimony.-
Beech Aircraft Corp. v. Rainey, 488 U. S., at 169 (citing Rules 701 to
705).  See also Weinstein, Rule 702 of the Federal Rules of Evidence
is Sound; It Should Not Be Amended, 138 F.R.D. 631, 631 (1991) (-The
Rules were designed to depend primarily upon lawyer-adversaries and
sensible triers of fact to evaluate conflicts-). Given the Rules'
permissive backdrop and their inclusion of a specific rule on expert
testimony that does not mention -general acceptance,- the assertion
that the Rules somehow assimilated Frye is unconvincing.  Frye made
`general acceptance' the exclusive test for admitting expert
scientific testimony.  That austere standard, absent from and
incompatible with the Federal Rules of Evidence, should not be applied
in federal trials.
                            B
  That the Frye test was displaced by the Rules of Evidence does not
mean, however, that the Rules themselves place no limits on the
admissibility of purportedly scientific evidence.  Nor is the trial
judge disabled from screening such evidence.  To the contrary, under
the Rules the trial judge must ensure that any and all scientific
testimony or evidence admitted is not only relevant, but reliable.
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