Opioid agonist treatment (OAT) is an effective method of addiction treatment and HIV prevention. However, globally, people who inject drugs (PWID) have insufficient OAT uptake. To expand OAT access and uptake, policymakers, program developers and healthcare providers should be aware of barriers to and facilitators of OAT uptake among PWID. METHODS: As a part of the HPTN 074 study, which assessed the feasibility of an intervention to facilitate HIV treatment and OAT in PWID living with HIV in Indonesia, Ukraine, and Vietnam, we conducted in-depth interviews with 37 HIV-positive PWID and 25 healthcare providers to explore barriers to and facilitators of OAT uptake. All interviews were audio-recorded, transcribed, translated into English, and coded in NVivo for analysis. We developed matrices to identify emergent themes and patterns. RESULTS: Despite some reported country-specific factors, PWID and healthcare providers at all geographic locations reported similar barriers to OAT initiation, such as complicated procedures to initiate OAT, problematic clinic access, lack of information on OAT, misconceptions about methadone, financial burden, and stigma toward PWID. However, while PWID reported fear of drug interaction (OAT and antiretroviral therapy), providers perceived that PWID prioritized drug use over caring for their health and hence were less motivated to take up ART and OAT. Motivation for a life change and social support were reported to be facilitators. CONCLUSION: These results highlight a need for support for PWID to initiate and retain in drug treatment. To expand OAT in all three countries, it is necessary to facilitate access and ensure low-threshold, financially affordable OAT programs for PWID, accompanied with supporting interventions. PWID attitudes and beliefs about OAT indicate the need for informational campaigns to counter misinformation and stigma associated with addiction and OAT (especially methadone).