This protocol outlines plans for conducting a mixed-methods systematic review on acute malnutrition in humanitarian crises. The review will investigate the relationship between recovery/cure and relapse, and between relapse and default and/or return defaults/episodes of default in the management of acute malnutrition in children under five in humanitarian emergencies. The review will also explore the contexts in which acute malnutrition management programmes were implemented, in order to identify and describe how context influences relapse and default and/or return default/episodes. This review is funded through the Humanitarian Evidence Programme, a UK Aid-funded partnership between Oxfam and Feinstein International Center (FIC) at the Friedman School of Nutrition at Tufts University. The Humanitarian Evidence Programme aims to synthesize evidence in the humanitarian sector and communicate the findings to stakeholders, with the ultimate goal of improving humanitarian policy and practice.