This campaign started in Greensboro, Alabama on the 1 February 1960.
Four black students ordered food at a white people only lunch counter and were refused service.
When asked to move they refused and returned to the same lunch counter the next day with dozens more protesters.
The idea of sit-ins spread quickly, by the start of 1961 it was estimated that around 700,000 people had taken part.
The sit-ins were broadcast throughout America on television news, gaining more publicity.
Many white people also showed solidarity with the black protesters and joined the sit-ins.