Anxiety and stress-related symptoms and disorders are prevalent and burdensome public health problems for which successful treatment remains limited. Following an overview of what anxiety and anxiety and stress-related disorders are, how we believe they develop, and how best to measure anxiety, this chapter summarizes the available evidence of the effects of exercise training on anxiety among healthy adults, chronically ill adults, and individuals diagnosed with an anxiety or stress-related disorder. The chapter concludes with a brief discussion of proposed mechanisms which may underlie relations of exercise and anxiety. The available evidence of exercise effects on anxiety continues to grow and currently supports that exercise training reduces anxiety symptoms among healthy adults, chronically ill patients, and patients with panic disorder. Preliminary data support that exercise training improves symptoms among patients with social anxiety disorder, generalized anxiety disorder, obsessive¿compulsive disorder, and posttraumatic stress disorder. Exercise-induced improvements appear to be comparable to empirically supported treatments for panic and generalized anxiety disorders. Larger trials should investigate the efficacy, generalizability, and biologically plausible mechanisms of exercise effects.