Only dysplastic (congenital) spondylolisthesis can lead to the complete picture of spondyloptosis. Its therapies are still con­ troversially discussed today. The therapeutic palette ranges from therapeutic nihilism to fusion in situ, to complete reduction of the lumbo-sacral junction. The goal of the symposium, which is presented in this book, was to demonstrate the anatomical and biomechanical fundamental principles which are significant for the selection of the appropriate therapy. With regard to the choice of therapeutic options, no unanimous opinion could be achieved. However, it clearly came to fruition that therapeutic nihilism is not indicated. It was also clearly pointed out that the fusion in situ cannot be considered as the therapy method of choice as progression of the slipping process can occur together with considerable neurological complications despite a long posterior fusion. A particular matter of concern of this symposium was to find out to what extent the local deformity influences the global sagittal profile which is of crucial signifi­ cance with regard to the biomechanical aspect of the lurnbo-sa­ cral hinge. This book is meant to be a guide to the various therapeutic concepts through which it has clearly emerged that cases of progressive isthmic-dysplastic spondylodesis should be opera­ tively treated as early as possible. Only then is it possible to re­ store the lumbo-sacral hinge and above all the position of the sacrum in an ideal way.