Respondent pleaded guilty in a Florida trial court to an indictment that included three capital murder charges. In the plea colloquy, respondent told the trial judge that, although he had committed a string of burglaries, he had no significant prior criminal record and that at the time of his criminal spree he was under extreme stress caused by his inability to support his family. The trial judge told respondent that he had "a great deal of respect for people who are willing to step forward and admit their responsibility." In preparing for the sentencing hearing, defense counsel spoke with respondent about his background, but did not seek out character witnesses or request a psychiatric examination. Counsels decision not to present evidence concerning respondents character and emotional state reflected his judgment that it was advisable to rely on the plea colloquy for evidence as to such matters, thus preventing the State from cross-examining respondent and from presenting psychiatric evidence of its own. Counsel did not request a presentence report because it would have included respondents criminal history and thereby would have undermined the claim of no significant prior criminal record. Finding numerous aggravating circumstances and no mitigating circumstance, the trial judge sentenced respondent to death on each of the murder counts. The Florida Supreme Court affirmed, and respondent then sought collateral relief in state court on the ground, inter alia, that counsel had rendered ineffective assistance at the sentencing proceeding in several respects, including his failure to request a psychiatric report, to investigate and present character witnesses, and to seek a presentence report. The trial court denied relief, and the Florida Supreme Court affirmed. Respondent then filed a habeas corpus petition in Federal District Court advancing numerous grounds for relief, including the claim of ineffective assistance of counsel. After an evidentiary hearing, the District Court denied relief, concluding that although counsel made errors in judgment in failing to investigate mitigating evidence further than he did, no prejudice to respondents sentence resulted from any such error in judgment. The Court of Appeals ultimately reversed, stating that the Sixth Amendment accorded [466 U.S. 668, 669] criminal defendants a right to counsel rendering "reasonably effective assistance given the totality of the circumstances." After outlining standards for judging whether a defense counsel fulfilled the duty to investigate nonstatutory mitigating circumstances and whether counsels errors were sufficiently prejudicial to justify reversal, the Court of Appeals remanded the case for application of the standards.

Held:

1. The Sixth Amendment right to counsel is the right to the effective assistance of counsel, and the benchmark for judging any claim of ineffectiveness must be whether counsels conduct so undermined the proper functioning of the adversarial process that the trial cannot be relied on as having produced a just result. The same principle applies to a capital sentencing proceeding - such as the one provided by Florida law - that is sufficiently like a trial in its adversarial format and in the existence of standards for decision that counsels role in the proceeding is comparable to counsels role at trial. Pp. 684-687.

2. A convicted defendants claim that counsels assistance was so defective as to require reversal of a conviction or setting aside of a death sentence requires that the defendant show, first, that counsels performance was deficient and, second, that the deficient performance prejudiced the defense so as to deprive the defendant of a fair trial. Pp. 687-696.

(a) The proper standard for judging attorney performance is that of reasonably effective assistance, considering all the circums