Who is a legal parent? I am writing a book that explores the complicated answer to this question.  It will examine the body of rules and doctrines that determine which adults—and how many of them—are entitled to parental rights, and which adults are saddled with parental obligations like child support.  This book will consider the historical development of parentage law; the social changes that have led to new questions and challenges; the growing gap between people’s expectations about their legal rights and obligations as parents (or gamete donors or gestational carriers) and the law’s actual assignment of those rights and obligations; and whether, given the wide variety of family forms today, it is possible to think about parentage as unified doctrine.  Topics addressed in depth include surrogacy, sperm and egg donation, posthumous conception, de facto parentage, adoption, unwed fatherhood, paternity misrepresentation, third-party visitation, and parentage by contract.