To obtain relief due to ineffective assistance of counsel, a criminal defendant must show that counsel's performance fell below an objective standard of reasonableness and that counsel's deficient performance gives rise to a reasonable probability that, if counsel had performed adequately, the result of the proceeding would have been different. Decided May 14, 1984 (argued January 10, 1984). Opinion of the Court: Sandra Day O'Connor → go there Dissenting: Marshall. Applied: the Sixth Amendment → go there Topic: Other rights regarding counsel. Strickland v. Washington, 466 U.S. 668 (1984), is a landmark Supreme Court case that established the standard for determining when a criminal defendant's Sixth Amendment right to counsel is violated by that counsel's inadequate performance. Wiki link