Mental health and psychosocial support (MHPSS) is a term used to describe a wide range of actions that address social, psychological and psychiatric problems that are either pre-existing or emergency-induced. These actions are carried out in highly different contexts by organizations and people with different professional backgrounds, in different sectors and with different types of resources. All these different actors--and their donors--need practical assessments leading to recommendations that can be used immediately to improve people's mental health and well-being. Although a range of assessment tools exist, what has been missing is an overall approach that clarifies when to use which tool for what purpose. This document offers an approach to assessment that should help you review information that is already available and only collect new data that will be of practical use, depending on your capacity and the phase of the humanitarian crisis. This document is rooted in two policy documents, the IASC Reference Group s (2010) "Mental Health and Psychosocial Support in Humanitarian Emergencies: What Should Humanitarian Health Actors Know?" and the "Sphere Handbook's Standard on Mental Health" (Sphere Project, 2011). It is written primarily for public health actors. As the social determinants of mental health and psychosocial problems occur across sectors, half of the tools in the accompanying toolkit cover MHPSS assessment issues relevant to other sectors as well as the health sector.