A crucial task for paleontologists and paleobiologists is the reconstruction of the appearance, movements, and behavior of extinct vertebrates from studies of their bones or other, more rarely preserved parts. A related issue is the boundary between the scientific evidence for reconstruction and the need to resort to imagination. In this book, sixteen paleontologists and biologists discuss these questions, review the current status of functional studies of extinct vertebrates in the context of similar work on living animals, and present a broad philosophical view of the subject's development within the framework of phylogenetic analysis. The authors describe and debate methods for making realistic inferences of function in fossil vertebrates, and present examples where we may be confident that our reconstructions are both detailed and accurate.