The book is the most in-depth account of the fossil skull anatomy and evolutionary significance of the 3.6-3.0 million year old early human species Australopithecus afarensis. Knowledge of this species is pivotal to understanding early human evolution, because 1) the sample of fossil remains of A. afarensis is among the most extensive for any early human species, and the majority of remains are of taxonomically informative skulls and teeth; 2) the wealth of material makes A. afarensis an indispensable point of reference for the interpretation of other fossil discoveries; 3) the species occupies a time period that is the focus of current research to determine when, where, and why the human lineage first diversified into separate contemporaneous lines of descent. Upon publication of this book, this species will be among the most thoroughly documented extinct ancestors of humankind. The book details the comparative anatomy of the new skull (and the cast of its brain, analyzed by R. Holloway and M. Huan) , as well as of other skull and dental finds recovered during the latest, ongoing field work at Hadar, and analyzes the evolutionary significance of A. afarensis in the context of other critically important discoveries of earliest humans made in recent years. In essence, it summarizes the state of knowledge about one of the central subjects of current paleoanthropological investigation.