This monograph of Electro-Optical E?ects to Visualize Field- and Current- Distributions in Semiconductors consists of ?ve parts, four of which are based ontheresearchofcadmiumsul?de,wherealargenumberofcontributionswere made between 1958 and the late 1960s to directly observe ?eld and current distributionsandinterprettheirresults.Thevisualizationof?elddistributions was accomplished by using the Franz Keldysh e?ect, and the visualization of currentinhomogeneitiesusestheshiftoftheopticalabsorptionedgebyJoule's heating. The ?fth part deals with a review of the explosively developing ?eld of N- and S-shaped current voltage characteristics causing inhomogeneities and instabilities in ?eld and current distributions. This part of the book was composed by Eckehard Sch. oll of the Technical University in Berlin. A major emphasis is given to the ?rst part of the book in which s- tionary high-?eld domains are described. These domains can be used as an essential tool to determine unambiguously certain semiconductor properties, such as the electron density and its mobility as the function of the actual electric ?eld. It is also helpful to determine changes of the work function and electron a?nities between di?erent materials, such as for electrodes and h- erojunctions. Finally, it gives direct information about certain doping and their spacial pro?le.