In recent years, a growing body of research has demonstrated that an individual's fitness level is a strong and independent marker of risk for cardiovascular and all-cause mortality. In addition, modest improvements in fitness through exercise intervention have been associated with considerable health outcome benefits. These studies have generally assessed fitness as a baseline marker in traditional epidemiological cohorts. However, there has been a recent recognition that fitness powerfully predicts outcomes associated with a wide range of surgical interventions. The concept of 'prehabilitation' is based on the principle that patients with higher functional capability will better tolerate a surgical intervention, and studies have shown that patients with higher fitness have reduced postoperative complications and demonstrate better functional, psychosocial, and surgery-related outcomes. This review focuses on the impact of fitness on surgical outcomes and provides a rationale in support of routine application of prehabilitation in the management of patients undergoing surgery.