Domestic resource mobilisation has become a high priority on the international development agenda, with building tax capacity integral to the achievement of the 2030 Agenda for Sustainable Development and the G20’s Tax agenda. This rapid review provides a mapping of the most prominent agencies and initiatives working on tax capacity building, identifying key work streams and areas of capacity building. The majority of the work on tax capacity building appears to be carried out through multi-stakeholder initiatives. This overview is not exhaustive, but it does provide a sample of the types of initiatives currently operational and some of the key actors in this area. The information presented in this report comes from the agencies and programmes themselves; we do not attempt to critically evaluate agencies or their programmes, or to locate programme evaluations.