This book has been conceived as a reference for all those who want to deepen their knowledge of technical details, design concept and interac­ tion of the individual modules of Zeiss operation microscopes. The sub­ jects of the book are classified in accordance with our intention. Special emphasis has been placed on practical hints for the user of opera­ tion microscopes to avoid operating errors. Parameters which are of para­ mount importance for surgeon and assistant such as PD and diopter set­ ting are therefore described in detail. The effects of wrong adjustments are indicated. The above statements also apply to the ample selection of acces­ sories for Zeiss operation microscopes. That is why much attention has been given to the accessories for co-observation and documentation. The most frequently used formulae are liste~ in the last chapter of the book, supplemented by nomograms which allow the reader to determine the most important data of a specific piece of microscope equipment without calculation. Our thanks are due to all those who assisted in preparing the manuscript, drawings and photographs, to Mrs. Ursula Gabler for making the English translation and Miss Helen Robertson for editing it, and last but not least to the Springer-Verlag for the most careful, qualified and excellent pro­ duction of the book.