The CAD tools in COMSOL Multiphysics® include many geometric primitives and operations for modeling the geometry using solid modeling and boundary modeling. This chapter covers geometry modeling in 1D, 2D, and 3D with examples of solid modeling, boundary modeling, Boolean operations, and other CAD tools. In addition, it shows how to use the tools for exploring geometric properties, such as volumes and surfaces. There is also information about using external CAD data and about adding and using geometries from the Part Libraries.