This Town Hall will provide an introduction to the GEOS-Chem model of atmospheric chemistry for new and prospective users, as well as an update on the latest model developments for experienced users. We will cover (1) the classic GEOS-Chem model; (2) the high-performance GEOS-Chem model; (3) GEOS-Chem as a chemical module for meteorological models including CESM and WRF; (4) using GEOS-Chem on the AWS cloud. Overview presentations on different aspects of the model will be given by the Model Scientist and Steering Committee members. There will be ample time for questions and for open discussion of model issues and development priorities.