The Cambridge Sports Union (CSU) is one of the premier athletic clubs in the Greater Boston area, with active sections for Running, Skiing, and Orienteering.

Founded in the 1960's, CSU has a long and storied history of participation in area, national, and international events, and boasts members from all corners of New England and beyond. CSU's running section hosts group runs and workouts throughout the year, including indoor and outdoor track workouts, hill and tempo runs, and long training runs in different Boston area locations. CSU runners participate in a variety of races including USATF-NE Grand Prix Races, the New England Runner Pub Series, the Mt. Washington Road Race and other mountain races, the BAA Marathon, and many more. CSU's Ski Section hosts a series of cross country ski races at the Weston Ski Track throughout the winter, and members compete in many other local and national events. CSU's Orienteering section hosts the popular Park-O Series at various locations in Cambridge and Boston.