In the 1960s, the US Government, as well as other countries, promoted the development and application of nuclear energy for the production of electric power. Pressurized water reactors (PWRs) are the most popular design, providing nearly two-thirds of the installed nuclear capacity throughout the world. For PWRs, the part of the coolant system that contains radioactivity is surrounded by a sturdy containment structure whose main purpose is to protect operating personnel and the public. Various auxiliary and safety systems attached to the primary are also located within the containment. This protected array of equipment we call the nuclear island is also called the “nuclear steam supply system” (NSSS). The principal operating data for current Westinghouse NSSS models are listed. The chapter describes the basic design and operating characteristics of a Westinghouse PWR plant. Differences from other manufacturers are mentioned if appropriate. Keep in mind that B&W and C-E made many of the domestic reactor vessels used by Westinghouse.