Recency assays use one or more biomarkers to identify whether HIV infection in a person is recent (usually within a year or less) or longstanding. Recency assays have been used to estimate incidence in representative cross-sectional surveys and in epidemiological studies to better understand the patterns and distributions of new and longstanding HIV infections. This technical guidance outlines best practices regarding the appropriate use of HIV recency assays for surveillance purposes and updates 2011 technical guidance from the World Health Organization (WHO) and the Joint United Nations Programme on HIV/AIDS (UNAIDS) on the use of HIV recency assays.