Urban populations living in informal settlements are inherently vulnerable to climate change, as informal settlements are characterized by overcrowding, poor-quality housing, lack of basic infrastructure, and poverty. Nevertheless, evidence of the associations among weather or climate and health in these populations is lacking, which severely constrains the design of climate change and disaster risk reduction adaptation strategies. To help fill this gap, this paper is a guide for researchers working on climate and health in informal settlements that summarizes key epidemiological methods and study designs commonly used in environmental health research. We focus on designs that have modest data requirements and that have been used successfully in resource-poor settings. The final section of the paper gives an overview of the current state of evidence about climate change and weather hazards in urban areas, as this is one of the main concerns for policymakers.