A concubine is a woman who lives with a man in a situation which is similar to marriage, although without all of the privileges of marriage. The term can refer simply to a woman who lives with a man without being married, although it usually specifically refers to a contracted state which establishes the concubine as a lesser member of a household which may already include other wives. Many cultures have a long history of concubinage and multiple wives, and this practice continues to be used in some parts of the world today.

The term comes from the Latin prefix com-, which means “with,” and cubara, “to lie down.” Both the Ancient Greeks and Romans had concubines, and concubinage also appears in the Christian Bible. These lesser wives were also widely found in Asia and the Middle East, and concubinal relationships can still be found in some of these regions, although they may be restricted by law.

Generally, only men of high social status have concubines. Additional wives require more wealth, especially since a well-outfitted concubine elevates a man's social status, while an obviously neglected concubine would reflect poorly upon him. Many concubines in Ancient China, for example, had their own homes along with numerous valuable possessions including elegant clothing and jewelry. Although these women did not enjoy the high status of the first wife of the household, they were still figures of respect, and major life events like childbirth and death were celebrated with lavish ceremonies.

Typically, the children of a concubine are recognized as official offspring of the concubine's partner, although they may not have access to the same privileges as the children of the first wife. The female children of concubines could be given in marriage to high ranking members of society to forge allegiances, or they could be kept around the family compound to serve the higher status wives and children. Male children might be encouraged to become civil servants or to take up positions as merchants. Like their mothers, these children would traditionally have been well cared for, since they were dependents of the head of the household.

The history of concubinage and its legal status is quite complex. In cultures where concubines were socially acceptable, their status was often dictated by various laws and social codes. These codes were designed to make the position of concubines and their children clear, and in some cases the laws also protected concubines from blatant abuse. Some famous examples of historical concubines include Hagar, Sarah's handmaiden who was given to Abraham in the Bible so that Sarah and Abraham could have a child, and the Fragrant Concubine, a legendary Chinese concubine.