Teachers at a preschool in Manhattan Beach, California, were falsely charged with the sexual abuse of schoolchildren, leading to the longest and costliest criminal trial in United States history.

Manhattan Beach is a city in southwestern Los Angeles County, California, United States, on the Pacific coast south of El Segundo, west of Hawthorne and Redondo Beach, and north of Hermosa Beach. As of the 2020 census, the population was 35,506.

The McMartin preschool trial was a day care sexual abuse case in the 1980s, prosecuted by the Los Angeles District Attorney, Ira Reiner. Members of the McMartin family, who operated a preschool in Manhattan Beach, California, were charged with hundreds of acts of sexual abuse of children in their care. Accusations were made in 1983, with arrests and the pretrial investigation taking place from 1984 to 1987, and trials running from 1987 to 1990. The case lasted seven years but resulted in no convictions, and all charges were dropped in 1990. By the case's end, it had become the longest and most expensive series of criminal trials in American history.