The Enforcement Act of 1871, also known as the Ku Klux Klan Act, Third Enforcement Act, Third Ku Klux Klan Act, Civil Rights Act of 1871, or Force Act of 1871, is an Act of the United States Congress that was intended to combat the paramilitary vigilantism of the Ku Klux Klan. The act made certain acts committed by private persons federal offenses including conspiring to deprive citizens of their rights to hold office, serve on juries, or enjoy the equal protection of law. The Act authorized the President to deploy federal troops to counter the Klan and to suspend the writ of habeas corpus to make arrests without charge.

The Ku Klux Klan, commonly shortened to the KKK or the Klan, is the name of several historical and current American white supremacist, far-right terrorist organizations and hate groups. According to historian Fergus Bordewich, the Klan was "the first organized terror movement in American history." Their primary targets, at various times and places, have been African Americans, Jews, and Catholics.