The nature and concept of "species" are central to paleontology, yet the resurgence of interest in species in evolutionary biology over the past few decades has had surprisingly little impact on how paleontologists think about species. Indeed, paleontological thinking about "species" is distractingly diverse. Are species real or not? Recognizable or not? How, if at all, are species based on fossils comparable to species based on modern organisms? The answers to all of these questions are diverse. Both questions and answers are especially important, however, given the theoretical role of species in modern paleobiology and macroevolution. This book aims to both summarize current paleontological thinking about species, and encourage additional explicit consideration about them.