Active surveillance is a solution to the widely acknowledged problem of overdiagnosis and overtreatment of clinically insignificant disease which accompanies early detection of prostate cancer using prostate-specific antigen (PSA) and biopsy. It is an approach to the management of favorable-risk prostate cancer which uses the opportunity provided by the long natural history of the disease to incorporate a period of initial observation into patient management. The basic concept is that most men diagnosed with low-grade, small-volume disease are not destined to have any clinical manifestations of the condition during their lifetime. However, a subset of patients with favorable-risk prostate cancer is at risk, due to either the presence of higher-risk disease not apparent at diagnosis or progression to a more aggressive phenotype over time. These patients can be identified with reasonable accuracy by close follow-up, including serial PSAs and biopsies, and treated effectively in most cases. The rationale, patient selection, method of follow-up, triggers for intervention, and recent results of this approach will be reviewed.