This is the first comprehensive synopsis of the biodiversity of Diptera, which with more than 150.000 described species contain more than one tenth of all described animal species. The first part is a review of what is already known, with treatments of all the major biogeographical regions and important archipelagoes; the second part contains case studies on open-ended taxa, Diptera as ecological indicators, and how to estimate the still unknown proportion of our fauna; and the third part discusses the digital and molecular tools needed to document the fauna. The book has an emphasis on principles and analytical approaches as well as on practical ‘how-to’ information and is intended for academicians and other professionals but with a significant outreach to students.