Fitness may relate to:
- Physical fitness, a general state of good health, usually as a result of exercise and nutrition
- Fitness approximation, model of the fitness function to choose smart search steps in Evolutionary algorithms including GA.
- Fitness and figure competition, a form of physique training, related to bodybuilding.
- In mathematics and computer science, the degree to which a given solution is optimized; see optimization (mathematics) or Fitness function
- Fitness (biology), an individual's ability to propagate its genes.
- FitNesse, a web server, a wiki, and a software testing tool.
- Fitness (magazine), a women's magazine, focusing on health and exercise.