This book could not have been written, if I had not had colleagues from industry and from compliance monitoring authorities, too numerous to mention them individually, with whom I could discuss any number of questions with respect to the actual and exact interpretation of the GLP Principles. The Quality Assurance people and the Study Directors from Industry who kept pestering us with the most complex and intricate questions about special situations and the interpretations of the GLP Principles with regard to these, the colleagues from the other Swiss Compliance Monitoring Authorities with whom many heated discussions arose around the industry questions, and the colleagues from the OECD Working Group on GLP, formerly the GLP Panel and its secretariat, headed by Dian Turnheim: To all of them I owe my sincerest thanks. Some of the material in this book was generously provided by Stan Woollen, Günther Menne, Rolf Vogel and Andreas Edelmann. Another important prerequisite for the successful completion of this book was the understanding of my wife, who constantly encouraged me and who, in consequence, bore patiently the innumerable evenings and weekends in the sole company of our cats, her favourite books (and the TV, if applicable), while her husband unsociably sat typing at the computer, and who, in the end, also helped greatly with the layout of the whole book.