The book provides a comprehensive introduction to the architecture of professional software systems. The first part discusses the roles of software architecture and presents fundamental structuring approaches as well as standard architectures. The following three parts detail the standard software layers: application, persistence, and presentation layers. Initially, the basic design goals, concepts, and errors, as well as the most important design patterns, are elaborated. Subsequently, various architectural variants are developed using an example to demonstrate the implementation of the concepts. For the presentation layer, a window interface is created using Java Swing and a web interface using Java Server Pages (JSP), while a simple framework is implemented for the persistence layer, utilizing Enterprise JavaBeans (EJB) technology.