Active surveillance for favorable risk prostate cancer has become increasingly popular in populations where prostate cancer screening is widespread, due to evidence that prostate cancer screening results in the detection of disease that is not clinically significant in many patients (i.e., untreated, would not pose a threat to health). This approach is supported by data demonstrating that patients who fall into the category of clinically insignificant disease can be identified with reasonable accuracy, and that patients who are initially classified as low risk who reclassify over time as higher risk and are then treated more aggressively are in most cases still cured. An active surveillance approach means (1) identifying patients who have a low likelihood of disease progression during their lifetime, based on clinical and pathologic features of the disease and patient age and comorbidity; (2) monitoring closely over time, (3) establishing reasonable criteria for intervention, which will both identify more aggressive disease in a timely fashion, and not result in excessive treatment, and (4) meeting the communication challenge to reduce the psychological burden of living with untreated cancer. The results of active surveillance, the criteria for patient selection, and the appropriate triggers for intervention are reviewed.