This publication addresses research questions related to an increase in the levels of access and utilization for four key interventions that have the potential to significantly reduce HIV infections among People Who Inject Drugs (PWID) and their sexual and injecting partners, and hence morbidity and mortality in low and middle-income countries (LMIC). These interventions are drawn from nine consensus interventions that comprise a 'comprehensive package' for PWID. The four interventions are: Needle and Syringe Programs (NSP), Medically Assisted Therapy (MAT), HIV Counseling and Testing (HCT), and Antiretroviral Therapy (ART). The book summarizes the results from several recent reviews of studies related to the effectiveness of the four key interventions in reducing risky behaviors in the context of transmitting or acquiring HIV infection. Overall, the four key interventions have strong effects on the risk of HIV infection among PWID via different pathways, and this determination is included in the documents proposing the comprehensive package of interventions. In order to attain the greatest effect from these interventions, structural issues must be addressed, especially the removal of punitive policies targeting PWID in many countries. The scientific evidence presented here, the public health rationale, and the human rights imperatives are all in accord: we can and must do better for PWID. The available tools are evidence-based, right affirming, and cost effective. What are required now are political will and a global consensus that this critical component of global HIV can no longer be ignored and under-resourced.