Exercise addiction is a controversial concept including whether excessive exercise is a positive or negative addiction and whether excessive physical activity could be harmful. The purpose of this chapter is to provide clarity to exercise addiction by reviewing the scientific literature examining its definition, measurement, correlates, prevention, and treatment. Exercise addiction is defined as a craving for leisure-time physical activity that results in uncontrollably excessive exercise behavior that manifests itself in physiological and/or psychological symptoms with two principal distinctions of primary and secondary addiction. Measuring exercise addiction involves the assessment of multidimensional characteristics that also consider symptoms of addiction and the ability to distinguish between low- and high-risk individuals for exercise addiction. Several risk factors for exercise addiction will be addressed including high levels of exercise identity, body dissatisfaction, neuroticism, extraversion and low levels of self-esteem and agreeableness. Finally, the scant literature on the prevention and treatment of exercise addiction will be reviewed. Given the lack of awareness in professional and lay communities about exercise addiction, healthcare professionals may not recognize the signs of exercise addiction even when its adverse health consequences are apparent.