CrossFit is a branded fitness regimen that involves constantly varied functional movements performed at high intensity. The method was developed by Greg Glassman, who founded CrossFit with Lauren Jenai in 2000, with CrossFit its registered trademark. The company forms what has been described as the biggest fitness chain in the world, with around 12,000 affiliated gyms in over 150 countries as of 2022, under half of which are located in the United States.

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 in CrossFit-affiliated 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; however, an article in the Journal of Sports Rehabilitation found that “the risk of injury from participation in CrossFit is comparable to or lower than some common forms of exercise or strength training”.