Box lacrosse is an indoor version of lacrosse played almost solely in Canada, chiefly in British Columbia and southern Ontario. The game is played in summer on an ice hockey rink from which the ice has been removed; the playing area is called the box, in contrast to the unenclosed playing field of outdoor lacrosse. Box lacrosse was invented in the 1930s as a way to promote business for ice hockey arenas, and quickly became the most popular version of the sport in Canada. Since 1935 the competition for the Mann Cup, Canada's most prestigious lacrosse trophy, has been conducted under box lacrosse rules.

In box lacrosse the goal is smaller (4' X 4') than in outdoor lacrosse (and the goaltender usually bigger). The attacking team must take a shot on goal within 30 seconds of gaining possession of the ball, and play is rougher than in the field game and in indoor lacrosse, a more recent code based on box lacrosse. Box lacrosse differs from the other two codes by allowing crosschecking (hitting another player with the stick with one's hands apart on the shaft) when playing the ball. It also allows solid wooden sticks, while indoor lacrosse permits only hollow metal sticks. These differences encourage passing over running.

A national senior men's lacrosse championship (the Mann Cup) has been awarded in Canada since 1901. It has been played under box lacrosse rules since 1935. A junior men's championship (the Minto Cup) has been awarded since 1937 (the Minto Cup was also awarded to a senior men's champion from 1901 to 1934).

In 1994 lacrosse was declared the Canadian national summer sport by act of Parliament (ice hockey is the national winter sport). Almost all summer lacrosse in Canada is played under box lacrosse rules.