Although the first description of patients with what we now call Crohn's disease or ulcerative colitis was published well before 1900, both disorders seem to be diseases of the twentieth century. At the very start of the twenty-first century, it therefore seems appropriate to look back and at the same time look forward and to assess what knowledge has been gained during the last 100 years and in what direction research and thereby clinical practice will go in the future. This book, the proceedings of Falk Symposium No. 111 held in Freiburg, Germany, on June 19-20 1999, contains contributions from experienced senior scientists on the state of the art in pathophysiology, diagnosis and treatment, together with unpublished and new findings from young researchers. Basic scientists and clinicians are thereby involved in an exchange of information which will lead to new directions for future research and clinical management of inflammatory bowel diseases.