There are more than two million adults incarcerated in the US and four million more on probation or parole. Rates of HIV are 8 to 10 times higher for incarcerated persons than for the general US population, hepatitis C rates are 9 to 10 times higher, and sexually transmitted disease (STD) rates among men entering jails are as high as 35%. Because many prisoners are serving short sentences for parole violation, and return to prison is common, at-risk individuals move frequently between prisons and their home communities. (National Commission on Correctional Health Care, 2002) There is an urgent need to develop effective, accessible HIV prevention programs and population-specific HIV education materials for prisoners and their partners. Despite this, institutional barriers have impeded development and evaluation of such programs. Prisoners in the US have virtually no access to condoms, bleach, clean syringes, comprehensive HIV prevention education or support for transitioning out of prison. Rules protecting the security of the institution also limit access by community-based organizations (CBOs) and researchers. Staff at Centerforce, a CBO, have provided comprehensive HIV prevention education at San Quentin State Prison since 1986. Since 1992 they have been evaluating many of these programs in collaboration with the Center for AIDS Prevention Studies (CAPS), UCSF.