Background: Medication-assisted treatment (MAT) is an effective method of addiction treatment and HIV prevention. However, globally, people who inject drugs (PWID) have insufficient MAT uptake. To expand MAT access and uptake, policy-makers, program-developers and health care providers should be aware of barriers to and facilitators of MAT uptake among PWID. Methods: As a part of the HPTN 074 study, which assessed the feasibility of an intervention to facilitate HIV treatment and MAT in PWID living with HIV in Indonesia, Ukraine, and Vietnam, we conducted in-depth interviews with 37 HIV-positive PWID and 25 health care providers to explore barriers to and facilitators of MAT 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 health care providers at all geographic locations reported similar barriers to MAT initiation, such as complicated procedures to initiate MAT, problematic clinic access, lack of information on MAT, misconceptions about methadone, financial burden, and stigma towards PWID. However, while PWID reported fear of drug interaction (MAT 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 MAT. 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 MAT in all three countries, it is necessary to facilitate access and ensure low-threshold, financially affordable MAT programs for PWID, accompanied with supporting interventions. PWID attitudes and beliefs about MAT indicate the need for informational campaigns to counter misinformation and stigma associated with addiction and MAT (especially methadone).