Marriage (conubium) was a fundamental institution of society in ancient Rome and was used by Romans primarily as a tool for interfamilial alliances. The institution of Roman marriage was a practice of marital monogamy: Roman citizens could have only one spouse at a time in marriage but were allowed to divorce and remarry. This form of prescriptively monogamous marriage that co-existed with male resource polygyny (powerful men can have one wife and many other sexual partners) in Greco-Roman civilization may have arisen from the relative egalitarianism of democratic and republican city-states. Early Christianity embraced this ideal of monogamous marriage by adding its own teaching of sexual monogamy, and propagating it worldwide to become an essential element in many later Western cultures.

Roman marriage had precedents in myth. The abduction of the Sabine women may reflect the archaic custom of bride abduction. Rome's Sabine neighbours rejected overtures of intermarriage by Romulus and his band of male immigrants. According to Livy, Romulus and his men abducted the Sabine maidens but promised them honorable marriage, in which they would enjoy the benefits of property, citizenship, and children.

Marriages helped families to build economic and political bonds and alliances. Matrimonium, the root of the English word matrimony, defined the role of wives as mothers (matres) who would produce legitimate children, as eventual heirs to their parents' estates. The most ancient form of marriage, traditionally reserved to the patrician social class, claimed the husband's right to control his wife and her property. In later developments, the bride retained control over her dowry; the resources of both parties formed a heritable estate.

During the Republican era, marriage, divorce and adultery were matters dealt with by the families concerned. Falling marriage and birth rates in the Later Republic and early Empire led to state intervention. Adultery was made a crime, for which citizen-women could be punished by divorce, fines and demotion in social status; men's sexual activity was adultery only if committed with a married citizen-woman. Families were also offered financial incentives to have as many children as possible. Both interventions had minimal effect.

Marriage (conubium) was one of the fundamental institutions of Roman society, as it joined not only two individuals but two families. The Romans considered marriage a partnership, whose primary purpose was to have legitimate descendants to whom property, status, and family qualities could be handed down through the generations.

The institution of marriage in ancient Rome was a strictly marital monogamy: under Roman law, a Roman citizen, whether male or female, could have only one spouse in marriage at a time but were allowed to divorce and remarry. The practice of marital monogamy that co-existed with male resource polygyny distinguished the Greeks and Romans from ancient civilizations in which elite males typically had multiple wives in the institution of marriage. Walter Scheidel believes that Greco-Roman monogamy in marriage may have arisen from the relative egalitarianism of the democratic and republican political systems of the city-states. The aspect of a marital monogamy was later embraced by early Christianity, which in turn perpetuated it with its own teaching of sexual monogamy as an ideal in later Western cultures. In the early fifth century Augustine referred to it as a "Roman custom".

Marriage had mythical precedents, starting with the abduction of the Sabine Women, which may reflect the archaic custom of bride abduction. Romulus and his band of male immigrants approached the Sabines for conubium, the legal right to intermarriage, from the Sabines. According to Livy, Romulus and his men abducted the Sabine maidens, but promised them an honorable marriage, in which they would enjoy the benefits of property, citizenship, and children.

Under Roman law, the oldest living male, the "father of the family" (pater familias), held absolute authority (patria potestas) over his children and, to a lesser extent, his wife. His household was thus understood to be under his manus (literally, "hand"). He had the right and duty to seek a good and valuable match for his children and might arrange a child's betrothal long before they came of age. To further the interests of their birth families, sons of the elite should follow their fathers into public life, and daughters should marry into respectable families. If a daughter could prove the proposed husband to be of bad character, she could legitimately refuse the match.