The WHO-UNHCR publication Assessing Mental Health and Psychosocial Needs and Resources: Toolkit for Humanitarian Settings was developed because of frequent requests from the field to advise on assessment. 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 that should help assessors review information that is already available and only collect new data that will be of practical use.