Non-mammalian synapsids were the dominant terrestrial vertebrates from the Late Carboniferous to the Middle Triassic and play a key role in understanding the origin and evolution of mammals. Despite these facts and the outstanding fossil record of the group, early synapsids remain obscure. This book showcases the full breadth of contemporary research on non-mammalian synapsids, ranging from taxonomy and phylogenetics to functional morphology, biogeography, paleoecology, and patterns of diversity. It also underscores the importance and potential of studying non-mammalian synapsid paleobiology in its own right, not just in the context of mammalian evolution.