This rapid review synthesises evidence on key aspects of mainstreaming institutional resilience and systems strengthening in donor policies and programming in FCAS (Fragile and Conflict-affect States) contexts, particularly in nutrition (food security), health, WASH and the economic sector. Institutional resilience is the ability of a social system (society, community, organisation) to absorb and recover from external shocks, while positively adapting and transforming to address long-term changes and uncertainty. Investing in strong, well-functioning and adaptable social systems, such as health, education and social protection systems, can build resilience, as this help to cushion the negative economic and social effects of crises. While development actors have established guidance on how institutions can be made more effective, inclusive and accountable, there is much less literature on institutional resilience and how development actors can help to foster it. Much of the literature notes a lack of systematic evidence on applying the concept of resilience. These gaps extend to a dearth of guidance on how development actors can mainstream institutional resilience and systems strengthening into their policies and programmes. This rapid review draws on common factors discussed in the literature that are considered important to the strengthening of resilience and particular systems. These may, in turn, provide an indication of ways in which to mainstream institutional resilience and systems strengthening into development policy and programmingFCDO (Foreign, Commonwealth and Development Office)