• Improvements in HIV service delivery are key to bringing countries closer to achieving the target of ending AIDS as a public health threat and situating HIV treatment and care as part of universal healthcare coverage. • The World Health Organization (WHO) guideline development process is recognized as one approach to identifying research gaps. Systematic reviews form the basis of recommendations formulated by an expert guideline development group, which is also tasked to identify research gaps. • The 2021 WHO HIV Service Delivery Guideline process identified 27 research gaps grouped into 8 areas where more research is needed to support enhancement and implementation of the new recommendations across the cascade of care. • Areas covered by WHO Service Delivery Guideline include antiretroviral therapy (ART) initiation outside the health facility, frequency of visits/refills, tracing and reengagement in care, assessing adherence, integration of HIV and sexual and reproductive health services, integration of HIV and diabetes and hypertension care, psychosocial interventions for adolescents, and task sharing of specimen collection and point-ofcare testing. • Key areas identified by the guideline process that could benefit from future research include tools to support ART initiation outside the health facility, outcomes of spacing of clinical visits/drug refills beyond 6 months, tailored support to minimize disengagement and support reengagement along the continuum of care, and accurate, feasible measures of adherence. • Strategies of integration of HIV and sexual and reproductive health services and hypertension and diabetes care, costs and cost-effectiveness of psychological support interventions, the performance of newer point-of-care technologies by nonlaboratory personnel, and the impact of diagnostic integration across disease types were also identified as key areas that would benefit from future research.