This book is based on the proceedings of the "International Working Conference on Model Realism" which was held in Bad Honnef near Bonn, April 20 - 23, 1982. ·Both its theme and format of discussion were unconventional. Their main motivation can be de scribed as follows: In the last several years there has been a growing interest in determining the ex tent to which different methodologies are able to adequately deal with real-world problems of contemporary interest, especially when people from different disciplines are involved in a large-scale project. The conference was to deal with the modeling aspects of different systems theories and approaches. It was intended to be a first step for an ongoing comparative discussion about the way in which methodologies can be used or be combined in order to contribute to systematic problem solutions. In order to get a common basis for a coherent and reliable discussion a set of 3 problem studies was introduced in the Call for Papers, each with a different back ground. They should provide a framework for a more detailed or specific problem de finition in a paper related to one of the problem studies. Slightly adjusted to the book format they are found ahead of the 3 main sections of this book each. The problem studies were constructed as modeling and organization/reorganization problem fields in the context of complex and large-scale real systems.