IGAC/SPARC Workshop on Global Chemistry-Climate Modeling and Evaluation; Davos, Switzerland, 21–24 May 2012 The study of chemistry-climate interactions represents an important focus of global change research. The interacting factors relating atmospheric chemistry and climate strongly couple the emerging issues of climate, stratospheric ozone depletion, and air quality, from both scientific and policy perspectives. Understanding how the chemistry and composition of the atmosphere may change over the 21st century is essential in preparing adaptive responses or establishing mitigation strategies. A changing atmosphere not only drives climate change but also directly impacts human health, agricultural productivity, and natural ecosystems. Provision of high-quality, policy-relevant information on the current state of climate and its possible future states, as well as options for mitigation, control, change, and adaptation, are thus strongly dependent on progress in modeling.