 Philosophical debate concerning marriage extends to what marriage, fundamentally, is; therefore, Section 1 examines its definition. Section 2 sets out the historical development of the philosophy of marriage, which shapes today’s debates. Many of the ethical positions on marriage can be understood as divided on the question of whether marriage should be defined contractually by the spouses or by its institutional purpose, and they further divide on whether that purpose necessarily includes procreation or may be limited to the marital love relationship. Section 3 taxonomizes ethical views of marriage accordingly. Section 4 will examine rival political understandings of marriage law and its rationale. Discussion of marriage has played a central role in feminist philosophy; Section 5 will outline the foremost critiques of the institution.