We combine theory and evidence on incubator and accelerator programmes and their effects on urban economic development. These structured co-working programmes have grown rapidly. However, a rich descriptive literature reveals little about their impact on participants or surrounding urban areas. We situate programmes in a conceptual framework of co-location tools, theorise objectives and benefits and report findings from systematic, OECD-wide reviews of the evaluation literature. These evaluations provide evidence that accelerators and incubators raise participant employment, with accelerators also aiding access to finance. Ecosystem features such as university involvement and urban economic conditions also influence programme outcomes. However, evaluation evidence is less clear on detailed intervention design. We consider wider lessons and lay out an agenda for future research.