PROJECT SUMMARY/ABSTRACT In this R21 application (PA-20-145: Innovations in HIV Prevention, Testing, Adherence and Retention to Optimize HIV Prevention and Care Continuum Outcomes), we propose to explore the use of community or home-based testing, including self-testing (HIVST) and preferences for linkage to confirmatory testing and treatment in cross- border migrants in Lesotho, a country with very high HIV prevalence as well as high rates of mobility. Through our research done as part of the Lesotho Population-based HIV Impact Assessment (LePHIA) in 2020, we found that Lesotho has made great gains in terms of HIV viral load suppression overall, but those who had recently migrated were significantly less likely to be virally suppressed, mainly due to lack of awareness. The Ministry of Health has been rolling out HIVST as a strategy to reach men and populations who do not normally access health care. However, an increase in testing is insufficient as a public health strategy if the barriers to treatment mean that knowledge of status does not translate into engagement in antiretroviral treatment and viral suppression, diminishing the clinical and epidemic control benefits. In order to determine the best strategy for increasing testing and linkage to treatment rates in migrants, we aim to determine preferences for confirmatory testing and treatment in cross-border migrants who report that HIV testing outside the facility is acceptable. First, we will conduct formative research to explore determinants of migrant health and to understand the barriers and facilitators to testing and accessing treatment or prevention in cross-border migrants, exploring preferences regarding location, types of services, and opportunities to use health services in South Africa. Second, we will contact participants in the LePHIA 2020 who identified as recent cross-border migrants and consented to be contacted for future research. Eligible participants will be invited to complete a discrete choice experiment (DCE) on their preferences for confirmatory testing after self- or other community-based testing, and linkage to treatment. The proposed study is innovative because it is the first known attempt to use a DCE in a diverse panel of cross-border migrants, recruited from the community rather than at health facilities. We will use findings to develop an intervention to support testing and linkage in cross-border migrants.