Wiggins v. Smith, 539 U.S. 510 (2003), is a case in which the United States Supreme Court spelled out standards for "effectiveness" in the constitutional right to legal counsel guaranteed by the Sixth Amendment.

Counsel's investigation of Wiggins' background was rudimentary and contained only a superficial knowledge of his history from a few sources, omitting the information in detailed social service reports of severe physical and sexual abuse.

The record of the sentencing proceedings suggests that counsel's failure to investigate the defendant's background stemmed from inattention, not strategic judgment.

He presented expert testimony by a forensic mental health specialist who described his personal history including the severe physical and sexual abuse he had endured and its effect upon him.

[4] The Supreme Court granted a new sentencing hearing, holding that Wiggins' Sixth Amendment right to effective assistance of counsel was violated.

[10] The Court further held that the counsel's decision in defending a client facing the death penalty must be based on a thorough investigation of all possible mitigating factors.

[3] The Supreme Court attempted to improve on the vague and generalized language in Strickland v. Washington by adding an American Bar Association Guideline 11.8.6.