The Tractatus Logico-Philosophicus was first published in 1921 under the title "Logisch-Philosophische Abhandlung"; a year later, it was released in a German-English version under the more common title. Since its publication, this sole book published by Wittgenstein himself has been regarded as difficult and enigmatic. For a logician like Russell, it seemed more a contribution to mysticism than to logic. It is not surprising that this book has been plagued by misunderstandings. Only gradually have the depth, significance, and philosophical dimensions of the text become apparent. The Tractatus is one of the few key texts of contemporary philosophy. Its importance for logic, philosophy of language, and metaphysics is greater than was suspected just two decades ago. The contributions in this volume are, with few exceptions, previously unpublished. They aim to provide a...