Against the background of debates about expanding HIV testing and counseling, we summarize the evidence on the social and behavioral dimension of testing and its implications for programs. The discrepancy between acceptance of testing and returning for results and the difficulties of disclosure are examined in light of research on risk perceptions and the influence of gender and stigma. We also summarize the evidence on the provision of testing and counseling, the implementation of practices regarding confidentiality and consent, and the results of interventions. We demonstrate that social factors have a considerable impact on testing, show that the services linked to testing are key determinants of utilization, and consider the implications of these findings for HIV testing programs.