Book excerpt: This text arose from a study originally undertaken for the Department of Energy to characterize the principal safety features of light water reactors of western design. This text should be of use to professional engineers interested in safety assessment of operating light water reactors, students interested in the principal safety features of LWRs, and others interested in tracing the design evolution of light water reactors. However, while ambitious in its scope, this text should not be viewed as presenting the levels of reactor safety of the various families of western reactor designs.