In the present book the Paleogene fossil record of birds is detailed for the first time on a worldwide scale. I have developed the idea for such a project for several years, and think that it is an appropriate moment to present a summary of our c- rent knowledge of the early evolution of modern birds. Meanwhile not only is there a confusing diversity of fossil taxa, but also significant progress has been made concerning an understanding of the higher-level phylogeny of extant birds. Hypotheses which were not considered even a decade ago are now well supported by independent analyses of different data. In several cases these group together morphologically very different avian groups and allow a better understanding of the mosaic character distribution found in Paleogene fossil birds. The book aims at bringing some of this information together, and many of the following data are based on first-hand examination of fossil specimens.