Climate change is a broad-reaching, global challenge. It impacts most human and natural systems, from agriculture and ecosystems to energy and health, and exacerbates other preexisting issues, from poverty to political instability. Evaluating these impacts and our vulnerability to them increases awareness of the need for adaptation and resilience. This chapter provides a brief history of impact assessments, focusing on the models, tools, and information that is needed and is available to quantify future impacts across a wide range of systems and scales and to provide valuable input to adaptation and resilience planning