This sourcebook provides step-by-step guidelines to conduct vulnerability assessments and monitor changes in vulnerability over time. It is structured along eight modules which provide detailed guidance on the operationalisation of a vulnerability assessment. The approach of the sourcebook is applicable from national to local level and to a broad range of sectors. It is illustrated with examples and lessons learned from pilot applications in Bolivia (Plurinational State of), Pakistan, Burundi and Mozambique, with a wide range of references to water scarcity and management.