Textbook in PDF format Using simple physical examples, this work by Erhard Scheibe presents an important and powerful approach to the reduction of physical theories. Novel to the approach is that it is not based, as usual, on a single reduction concept that is fixed once and for all, but on a series of recursively constructed reductions, with which all reductions appear as combinations of very specific elementary reductions. This leaves the general notion of theory reduction initially open and is beneficial for the treatment of the difficult cases of reduction from the fields of special and general relativity, thermodynamics, statistical mechanics,and quantum mechanics, which are treated in the second volume. The book is systematically organized and intended for readers interested in philosophy of science as well as physicists without deep philosophical knowledge. Front Matter The Problem Physical Theories Corroboration and Empirical Progress Exact Reductions Approximate Reductions Partial Reductions Back Matter