This paper introduces the analyses of the potential impacts of climate change on the city of Chicago and the Great Lakes region and potential response options that provide the basis for this special issue. Covering projected changes in climate and hydrology, this collection of studies first estimates the potential impacts of climate change on human health, natural ecosystems, water resources, energy, and infrastructure in the city of Chicago and the surrounding Great Lakes region. A consistent set of future climate projections have been used as the basis for each analysis, which together provide a vivid impression of the consequences likely to result under the SRES higher (A1FI) as compared to the lower (B1) emission scenarios. These findings highlight the importance of the next set of analyses, which focus on quantifying Chicago's greenhouse gas emissions and prioritizing emissions reduction and adaptation options in light of the projected impacts. Together, these analyses form the basis for the City of Chicago's Climate Action Plan, the first such plan to be based on a thorough climate change impact assessment exploring the implications of a range of future climate scenarios. Although focused on Chicago and the Great Lakes region, the methods described here are generally applicable across North America and many other parts of the world, serving as a pattern for future regional assessments to directly inform adaptation and mitigation policy at the local to regional scale.