The overall purpose of Human Embryos, Human Beings is to establish the ontological status of the human embryo, in light of the most recent biological evidence. The thesis of the book is that sound philosophical reasoning and the available scientific evidence support the claim that a human being is present from the moment of fertilization onward (the “immediate hominization” view) and does not support the contrary claim that a human being appears only after a time following fertilization (the “delayed hominization” view). Included in the scope of this argument is an examination of several long-standing philosophical arguments claiming that immediate hominization is false; a detailed examination of several arguments claiming that though immediate hominization is possible, both evidence and argument best support the delayed hominization view or some alternate view; and an examination of several cases where natural defect or scientific manipulation make determining the ontological status of the embryo more difficult. The book also includes a presentation of hylomorphism, as this is the philosophical viewpoint employed by the authors to analyze the question. Human Embryos, Human Beings is based on the premise that philosophical and scientific approaches are not in conflict, with the most comprehensive understanding of human embryos being achieved by application of a rigorous hylomorphic philosophy to the best available scientific data. Often, one finds either a thorough and well-reasoned philosophical account or a detailed scientific account. This book makes a welcome addition to the field by integrating both of these needed elements into a single text.