The Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) is primarily designed to characterize radiative forcings in the Climate Model Intercomparison Project phase 5 (CMIP5) historical and future climate simulations, and to provide diagnostics to facilitate understanding of differences in those forcings between models. Most of the participating ACCMIP models were also used in CMIP5 simulations. The primary emphasis is on tropospheric ozone and aerosols, both of which have substantial climate forcing that varies widely in space and time. ACCMIP includes extensive evaluations of the models against observations. Papers cover a wide variety of analyses, including studies of ozone, methane, hydroxyl radical, and multiple aerosol types, their role in issues from climate change to air quality in the past and future, and evaluation against remote sensing data, in situ observations, and ice cores.