 Models of the climate system, especially computer simulation models, have come to occupy a central place in both theoretical and applied research in climate science. After providing an overview of some common types of climate model  (Section 4.1),  this section focuses primarily on atmosphere-ocean general circulation models and earth system models, discussing some noteworthy features of their construction  (Section 4.2),  some of their most important uses  (Section 4.3),  and how they are evaluated  (Section 4.4).  The focus is on these complex climate models both because they have attracted the most attention from philosophers and, relatedly, because they play particularly important roles in climate research today, including climate change research.