Climate change is one of the most urgent challenges for people and ecosystems worldwide. The recently published sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) stresses the occurrence of widespread adverse impacts of climate change. Increased frequency and intensity of extreme weather events, as well as slow-onset processes cause enormous losses and damages to human and natural systems. Marginalized groups and people in vulnerable situations are often disproportionally affected. While the impacts of climate change already become more tangible and threatening, action for addressing them remains insufficient. Adaptation to climate change is, thus, becoming a necessity for governments, companies, and private citizens. To provide practical and scientifically sound guidance on how to conduct vulnerability assessments, GIZ published its Vulnerability Sourcebook in 2014. The Vulnerability Sourcebook was used in over twenty different GIZ partner countries and provides a step-by-step guidance for designing and implementing a vulnerability assessment. It is also one of the methodological foundations for the ISO 14091:2021 standard on vulnerability, impacts and risk assessment for climate change adaptation.