The Boston Marathon is an annual marathon hosted by several cities in greater Boston in eastern Massachusetts, United States. It is always held on Patriots' Day, the third Monday of April. Begun in 1897, inspired by the success of the first marathon competition in the 1896 Summer Olympics, the Boston Marathon is the world's oldest annual marathon and ranks as one of the world's best-known road racing events.

Women were not allowed to enter the Boston Marathon officially until 1972. Roberta "Bobbi" Gibb is recognized by the race organizers as the first woman to run the entire Boston Marathon (in 1966). In 1967, Kathrine Switzer, who had registered as "K. V. Switzer", was the first woman to run and finish with a race number. She finished despite an infamous incident in which race official Jock Semple tried to rip off her numbers and eject her from the race. In 1996 the B.A.A. retroactively recognized as champions the unofficial women's leaders of 1966 through 1971.

In 2015, about 46 percent of the entrants were female.

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