This paper explores the evidence base for services designed to meet the needs of people who experience homelessness and use drugs (PEHAD). Through a delimited analysis of existing systematic and rapid evidence reviews, it considers the key lessons for the development of effective homelessness services in Europe. The aims of the paper are twofold. Its first objective is to identify the gaps and limitations in our understanding of what constitutes homelessness, as well as the holes in the existing evidence base around service provision for those experiencing homelessness. The second goal is to draw on the available research to explore what is available in terms of practical knowledge transfer, i.e. evidence that might enhance homelessness prevention and services.