One of social protection’s primary roles is to help individuals and households cope with shocks that affect entire communities or large population groups at the same time (e.g. economic crises, disasters associated with extreme weather events and conflict-related shocks). In such circumstances, the effectiveness of social protection response hinges critically on timeliness, adaptability and adequacy. Policy needs rapid implementation at a large enough scale to reach the high number of people affected. This report reviews the potential advantages and limitations of the inclusion of index-based triggers in social protection programmes against the objective of effective covariate shock response. It analyses ten social protection programmes with an index-based trigger component, identifies the variations in their design features and analyses the evidence on their effectiveness where they have been activated.