This book is the proceedings of the Falk Symposium No. 121 on 'Steatohepatitis (NASH and ASH)', held in Den Haag, The Netherlands, on October 14-15, 2000. The histological features of what we now call non-alcoholic steatohepatitis were described as early as 1962 by the Honorary President of the Symposium, Professor Herbert Thaler, from Vienna. Others followed, and in 1980 Jürgen Ludwig, one of the speakers of this symposium, introduced the name `non-alcoholic steatohepatitis' or NASH. In a Consensus Symposium organized by the National Institute of Health (NIH) in Washington, USA, in December 1998, NASH was recognized as one of the most common liver diseases in Western countries when viral hepatitis and heavy alcohol consumption were excluded. ASH, or alcoholic steatohepatitis, is more common than NASH, since alcohol is omnipresent in Western as well as Eastern cultures. Histologically NASH and ASH are similar or even identical. Morphological findings range from fatty degeneration to inflammation and fibrosis, and may end up in liver cirrhosis. In spite of the well-defined morphological features, our knowledge of epidemiology, aetiology, and pathogenesis is full of gaps, especially for NASH. Therefore, it is the purpose of this book to show the state of the art, to discuss recent scientific data, and to suggest possible treatment strategies, hoping to stimulate clinicians as well as scientists.