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Half the world's population has access to Internet and technologies, and utilization is near-ubiquitous among providers and key populations. Despite being so well connected; identifying, reaching and linking vulnerable populations to HIV clinical services remains a global challenge. This review highlights the emerging online-to-offline (O2O) models, their potential in scaling up services, and evaluating impact, and implications for future research.Globally, four major types of O2O models have been implemented, primarily in the West and Asia, especially among MSM and transgender women. These models have varying levels of impact in terms of reach, engagement, participation, linkage, and ability to track and monitor participants, and assess outcomes. Those integrated with offline sites enable seamless transition, dramatically reduce the O2O linkage time and demonstrate high linkage success (>73%). O2O models are ideal for at-risk, stigmatized, criminalized populations and for scaling-up biomedical prevention interventions such as preexposure and postexposure prophylaxis.O2O models represent novel and powerful solutions to reverse the pandemic and could help fill significant programmatic gaps in tracking individuals through HIV cascades. Providers, especially in resource-limited settings, could choose between a variety of current approaches highlighted in this review and employ no-cost or cost-effective technologies to transform their traditional models and leverage O2O models.