We use geometry to describe the objects that occupy a scene in space, whether they are as simple as triangles, boxes, and pyramids, or as complex as teapots, horses, and clouds. In addition to being described by its geometry, an object has an appearance such as color, opacity, and texture. Complex objects are made of parts, and each part may have its own appearance. Even in the case of a simple cube, each side may be painted a different color. It follows that geometry and appearance are often closely linked. We explore these topics in this section.