This relatively short chapter introduces the physical features of a coral reef. A view from shore, aerial photographs, and a diagram show the appearance of the reef and how the features of a reef vary with water depth. The nature of corals is introduced, along with the fact that the symbiotic zooxanthellae in their tissues allow the corals to grow massive skeletons that in fact are what builds the reef. The difference between the fringing reefs of the Caribbean and the coral atolls is discussed. The concept of zonation of the kinds of corals on the reef is introduced. In the shallowest zone, where the wave action is the strongest, Acropora palmata builds massive structures that can withstand the pounding of the waves, while slightly deeper, the less robust Acropora cervicornis defines a zone. To conclude the chapter, several photographs of underwater ‘landscapes’ show scenes of different parts of the reef, from the reeftop and its assemblage of corals to the sloping fore-reef and a sand channel between deep reef patches.