Climate change is expected to be the most challenging public health issue of the 21st century and healthcare systems will be impacted by climate-driven emergencies. Durham Region is already experiencing the effects of climate change, yet most residents do not believe they will be harmed by it in their lifetime. There is a clear need to understand and communicate the near and long-term health consequences of climate change. As part of our mandate under the Ontario Public Health Standards, the Durham Region Health Department (DRHD) initiated a series of climate change and health vulnerability assessments (CCHVAs) to identify current and future health impacts of climate change related to extreme heat, extreme weather, poor air quality, vector-borne disease, ultraviolet radiation, food and water, and mental health (see Figure 1.1). These assessments will provide valuable information to decision makers, municipalities, community organizations and residents to recognize, respond to and reduce climate related health impacts. This primer serves as a background reference document for the vulnerability assessments by providing: • a global and local overview of climate change and related health impacts; • an equity focussed framework for defining, assessing and addressing climate vulnerability; • a summary of the approach undertaken to complete the assessments; and, • local environmental and community features relevant to assessing climate-related health risks.