The Know Nothings were a nativist political movement in the United States in the 1850s, officially known as the Native American Party before 1855, and afterwards simply the American Party. Members of the movement were required to say "I know nothing" whenever they were asked about its specifics by outsiders, providing the group with its colloquial name. The Know Nothing movement briefly emerged as a major political party in the form of the American Party.

The new party name was in reference to members' beliefs that non-immigrants were what they called Native Americans; later parties by the same name were not affiliated with this movement. The movement organized in various social clubs and political forums across the country and created propaganda to draw adherents to their cause. Many 1856 Know Nothing adherents also voted in support of the fledgling Republican Party, which had started to court this demographic by campaigning around anti-Popery and bans on immigration.