Not intended as a textbook of adverse drug reactions but rather as a way to elucidate the methods of investigating adverse drug reactions as well as other questions of drug effects. Section one gives an introduction to the field and presents basic scientific principles of clinical epidemiology. In this edition a chapter has been added on analogous basic principles of clinical pharmacology. A presentation of multiple different perspectives on clinical epidemiology can be found in the second section. Due to major new methodological developments in the field, sections three and four have had new chapters added and others removed. The first three sections will be of interest to the neophyte while sections two through four will appeal to those with some background who want a more in-depth view of the field.