Cite as: 539 U. S. 510 (2003)
Opinion of the Court
cation must have been "objectively unreasonable." See Williams v. Taylor, 529 U. S., at 409.
We established the legal principles that govern claims of ineffective assistance of counsel in Strickland v. Washington, 466 U. S. 668 (1984). An ineffective assistance claim has two components: A petitioner must show that counsel's performance was deficient, and that the deficiency prejudiced the defense. Id., at 687. To establish deficient performance, a petitioner must demonstrate that counsel's representation "fell below an objective standard of reasonableness." Id., at 688. We have declined to articulate specific guidelines for appropriate attorney conduct and instead have emphasized that "[t]he proper measure of attorney performance remains simply reasonableness under prevailing professional norms." Ibid.
In this case, as in Strickland, petitioner's claim stems from counsel's decision to limit the scope of their investigation into potential mitigating evidence. Id., at 673. Here, as in Strickland, counsel attempt to justify their limited investigation as reflecting a tactical judgment not to present mitigating evidence at sentencing and to pursue an alternative strategy instead. In rejecting the respondent's claim, we defined the deference owed such strategic judgments in terms of the adequacy of the investigations supporting those judgments:
"[S]trategic choices made after thorough investigation of law and facts relevant to plausible options are virtually unchallengeable; and strategic choices made after less than complete investigation are reasonable precisely to the extent that reasonable professional judgments support the limitations on investigation. In other words, counsel has a duty to make reasonable investigations or to make a reasonable decision that makes particular investigations unnecessary. In any ineffectiveness case, a particular decision not to investigate must be directly assessed for reasonableness in all the circum-
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