In 1978, the U.S. Supreme Court held in Monell v. New York Dept. of Social Services that municipalities could not be held vicariously liable under 42 U.S.C. section 1983 for their employees' violation of constitutional rights. Instead, to hold the municipality liable, the plaintiff had to prove that a custom, policy, or practice of the municipality caused the constitutional violation.
Los Angeles County v. Humphries, published November 30, 2010, resolved a split between the circuits on whether Monell applies only to suits for damages. In Humphries, the U.S. Supreme Court held that Monell's "custom, policy, or practice" requirement applies in section 1983 cases whether the relief sought is monetary or prospective (such as injunctive or declaratory relief). The high court reversed the Ninth Circuit's decision to the contrary.