A domestic partnership is a legal or personal relationship between two individuals who live together and share a common domestic life but are neither joined by a traditional marriage nor a civil union. However, in some jurisdictions, such as California, domestic partnership is in fact equivalent to marriage, or to other legally recognized same-sex or different-sex unions. The terminology for such unions is still evolving, and the exact level of rights and responsibilities conferred by a domestic partnership varies widely from place to place.

Some legislatures have voluntarily established domestic partnership relations by statute instead of being ordered to do so by a court. Although some jurisdictions have instituted domestic partnerships as a way to recognize same-sex unions, domestic partnerships may involve either different-sex or same-sex couples.

In some legal jurisdictions, domestic partners who live together for an extended period of time but are not legally entitled to common-law marriage may be entitled to legal protection in the form of a domestic partnership. Some domestic partners may enter into domestic partnership agreements in order to agree contractually to issues involving property ownership, support obligations, and similar issues common to marriage.

One of the purposes of domestic partnership relation is to recognize the contribution of one partner to the property of the other. In the common law, devices such as the constructive trust are available to protect spouses in legal or common-law marriages. In civil law jurisdictions, such trusts are generally not available, prompting courts to find alternative ways to protect the partner who contributes to the other's property.