This is the part of any book where the authors usually discuss why they wrote it. We hope, however, that the text will justifY itself. In fact, any well-trained ecologist will immediately grasp the significance of these seminal works. We have therefore tried to keep our interpretive comments to a minimum. Students of "modern" theoretical ecology will want to contrast the papers in this collection with their modern derivatives. We believe that those who do so will be surprised, if not amazed, by the ecological sophistication and intellectual power of the earlier works. They will stand as a challenge to those who study them, and we hope, provide a standard for the quality of their work. By presenting this collection of works, most of them not easily available and/or for the first time in English, we hope to help them attain the high level of recognition they deserve. We are also enabling readers not sufficiently familiar with Italian to acquire enough of a background to properly follow the works in French not presented here by including Volterra's "Variazioni e fluttuazioni del numero d' indi vidui in specie animali convi venti" (1927), still available. in the original edition.