The earth, viewed through the window of an airplane, shows a regularity and reptition of features, for example, hills, valleys, rivers, lakes, and forests. Nevertheless, there is great local variation; Vermont does not look like Utah. Similarly, if we rise above the details of a few programming languages, we can discern features that are common to many languages. This is the programming language landscape; the main features include variables, types, control structures, and input/output. Again, there is local variation; Pascal does not look like Basic. This work is a broad and comprehensive discussion of the principal features of the major programming languages. A Study of Concepts The text surveys the landscape of programming languages and its features. Each chapter concentrates on a single language concept. A simple model of the feature, expressed as a mini-language, is presented. This allows us to study an issue in depth and relative isolation. Each chapter concludes with a discussion of the way in which the concept is incorporated into some well-known languages. This permits a reasonably complete coverage of language issues.