This anthology consists of a collection of papers on the nature of dis- positions and the role of disposition concepts in scientific theories. I have tried to make the collection as representative as possible, except that problems specifically connected with dispositions in various special sciences are relatively little discussed. Most of these articles have been previously published. The papers by Mackie, Essler and Trapp, Fetzer (in Section 11), Levi, and Tuomela appear here for the first time, and are simultaneously published in Synthese 34, No. 4, which is a special issue on dispositions....