oceanCommunity Earth System Model (CESM) belongs to an elite category of computer-based simulation models known as general-circulation models. Such models use mathematical formulas to recreate the chemical and physical processes that drive Earth’s climate. What emerges from trillions of computer calculations is a picture of the world’s climate in all its complexity. The Ocean Model Working Group was formed to discuss issues related to ocean components in the CESM context and to coordinate the development and testing of ocean components.