The programming language Oberon is the result of a concentrated effort to increase the power of Modula-2 and simultaneously to reduce its complexity. Several features were eliminated, and a few were added in order to increase the expressive power and flexibility of the language. This paper describes and motivates the changes. The language is defined in a concise report. Introduction The programming language Oberon evolved from a project whose goal was the design of a modern, flexible, and efficient operating system for a single-user workstation. A principal guideline was to concentrate on properties that are genuinely essential and - as a consequence - to omit ephemeral issues. It is the best way to keep a system in hand, to make it understandable, explicable, reliable, and efficiently implementable. Initially, it was planned to express the system in Modula-2 [1] (subsequently called Modula), as that language supports the notion of modular design quite effectively, and because an oper...