Abortion remains a highly controversial issue in many countries and subject to intense public debate. The aim of this chapter is to summarize the most prominent assumptions and arguments concerning the moral and legal dimensions of abortion on which this debate rests. Where the moral justifiability of abortion is concerned, this chapter focuses on arguments relating to the moral status of the fetus or embryo, the notion of personhood, the biological development of the embryo or fetus, and the moral relevance of specific points in the developmental process. In terms of the legal aspects, we consider concepts and principles invoked at law, principally, the rights of pregnant women and the medical concept of viability. For each moral and legal position in the abortion debate, we provide an overview of the principal assumptions and arguments and acknowledge the main criticisms.