Under funding from the National Institute on Drug Abuse, the UCLA Integrated Substance Abuse Programs (ISAP), in collaboration with Walden House and the California Department of Corrections and Rehabilitation, is conducting a five-year study that will involve a randomized test of the use of incentives with parolees in a community-based residential substance abuse treatment to increase treatment admission and treatment retention, and thereby increase the likelihood of improved outcomes. Study participants will be recruited from clients in a prison-based treatment program who have a referral to the Walden House community program. The Admission Phase of the study assesses the effect of an incentive (voucher) on enrolling in the Walden House program. The Attendance Phase assesses the effect of incentives on treatment attendance and on post-treatment drug use, crime, and psychosocial behaviors, including HIV risk behaviors. In addition, an incentive protocol will test whether an incentive will encourage participation in HIV testing and counseling. The intervention will last for six months.