People who use drugs are at increased risk for HIV acquisition, poor engagement in health care, and late screening for HIV with advanced HIV at diagnosis and increased HIV-related morbidity, mortality, and health care costs. This systematic review evaluates current evidence about the effectiveness and feasibility of implementing HIV testing in U.S. substance use treatment programs. The literature search identified 535 articles. Full text review was limited to articles that explicitly addressed strategies to implement HIV testing in substance use programs: 17 met criteria and were included in the review; nine used quantitative, qualitative, or mixed-method designs to describe or quantify HIV testing rates, acceptance by clients and staff, and cost-effectiveness; eight organization surveys described barriers and facilitators to testing implementation. The evidence supported the effectiveness and feasibility of rapid, routine, and streamlined HIV testing in substance use treatment programs. Primary challenges included organizational support and sustainable funding.