The Birthday of Martin Luther King, Jr. , often called Martin Luther King Day, is a United States holiday honoring the Reverend Dr. Martin Luther King, Jr., observed on the third Monday of January each year, around the time of King's birthday, January 15. It is the only United States federal holiday commemorating an African American and one of only four to commemorate an individual person.

Martin Luther King Day was founded as a holiday promoted by labour unions in contract negotiations. After King's death in 1968, Rep. John Conyers introduced a bill in Congress to make King's birthday a national holiday, highlighting King's activism on behalf of trade unionists. Unions did most of the promotion for the holiday throughout the 1970s. In 1976, trade unionists helped to elect Jimmy Carter, who endorsed the King Day bill. After that endorsement, union influence in the King holiday campaign declined, and the King Center turned to support from the corporate community and the general public. The success of this strategy was cemented when musician Stevie Wonder released the single "Happy Birthday" to popularize the campaign in 1980 and hosted the Rally for Peace Press Conference in 1981. 6 million signatures were collected for a petition to Congress to pass the law, termed by a 2006 The Nation article as "...the largest petition in favor of an issue in US history."