Stack v. Boyle, 342 U.S. 1 (1951), was a United States Supreme Court case involving the arrest of members of the Communist Party who were charged with conspiring to violate the Smith Act. The case regards the Eighth Amendment issue of excessive bail.

The Eighth Amendment to the United States Constitution protects against imposing excessive bail, excessive fines, or cruel and unusual punishments. This amendment was adopted on December 15, 1791, along with the rest of the United States Bill of Rights. The amendment serves as a limitation upon the state or federal government to impose unduly harsh penalties on criminal defendants before and after a conviction. This limitation applies equally to the price for obtaining pretrial release and the punishment for crime after conviction. The phrases in this amendment originated in the English Bill of Rights of 1689.