As HIV diagnoses continue to decrease and rates of viral suppression increase in the United States, key populations of underserved individuals represent a disproportionate share of those left undiagnosed, unengaged in care, and not virally suppressed. In 2021, the Health Resources and Services Administration's HIV/AIDS Bureau funded 20 HIV care organizations across the United States to implement seven innovative evidence-based interventions to engage individuals in the following four focus areas: LGBTQ+ youth, people with substance-use disorder, individuals with incarceration experience, and those for whom telehealth may reduce barriers to care. This article explores themes of implementer experiences common across interventions serving the four focus areas. Data sources include key informant interviews (