Active surveillance for favorable risk prostate cancer has become increasingly popular in populations where prostate cancer screening is widespread, because of 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 showing 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 reclassified over time as higher-risk and are treated radically are still cured in most cases. Active surveillance 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) close monitoring over time; 3) developing reasonable criteria for intervention, which will 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. This article reviews the results of active surveillance, the criteria for patient selection, and the appropriate triggers for intervention.