CrossFit is a branded fitness regimen that involves constantly varied functional movements performed at high intensity. The methodology was developed by Greg Glassman, who founded CrossFit, LLC, with Lauren Jenai in 2000, with CrossFit its registered trademark.

CrossFit is promoted as both a physical exercise philosophy and a competitive fitness sport, incorporating elements from high-intensity interval training, Olympic weightlifting, plyometrics, powerlifting, gymnastics, kettlebell lifting, calisthenics, strongman, and other exercises. It is practiced by members of thousands of affiliated gyms, roughly half of which are located in the United States, and by individuals who complete daily workouts (otherwise known as “WODs” or “Workouts of the Day”).

CrossFit has been criticized for causing more injuries than other sporting activities such as traditional weightlifting, although a review of scientific literature has found injury rate with CrossFit to be comparable or lower than other sports including Olympic weightlifting. There are also concerns that its methodology may cause exertional rhabdomyolysis, a possible life-threatening breakdown of muscle from extreme exertion.