The Geoengineering Model Intercomparison Project (GeoMIP) has been highly successful in identifying robust climate model response to various geoengineering scenarios. There are currently seven core GeoMIP simulations, with another four submitted as GeoMIP's contribution to CMIP6. These experiments evaluate model response to various forms of geoengineering, focusing on solar dimming, stratospheric sulfate aerosol injections, marine cloud brightening via sea spray, and cirrus cloud thinning. In this special issue, we examine results from these simulations that have been conducted by 15 climate modeling centers from around the world. The results presented here provide a key source of information about the range of potential climate effects from geoengineering, any possible unintended side effects that geoengineering may cause, and the efficacy of geoengineering as a response to climate change. These simulations also reveal fundamental climate responses to radiative forcing, illuminating various feedback processes and interactions between different components of climate models.