Domestic partner or domestic partnership identifies the personal relationship between individuals who are living together and sharing a common domestic life together but are not joined in any type of legal partnership, marriage or civil union. Some legal jurisdictions recognize that individuals who live together after a long period of time, while not entitled to common-law marriage status may be entitled to some protection under the legal concept of domestic partnership. In some places parties that live together enter into domestic partnership agreements in order to contractually agree to certain issues between them in relation to joint property ownership, support obligations and similar issues to that found in marriage. See effects of marriage and palimony.

In some jurisdictions domestic partnerships are created by statute rather than having been the invention of judicial decisions. One of the reason for the creation of the relation of domestic partnership is to recognize the contribution of one partner to the property of the other. In the common law such devices such as the constructive trust are available to protect spouses, in legal marriage or in common-law marriage. In civil law jurisdictions this type of legal concept is generally not available so courts have tried to find alternative ways to protect the partner who has contributed to the other partner's property.

Some jurisdictions have instituted domestic partnerships as a way to recognize same-sex unions. See also same-sex marriage.

On September 4, 2003 the California legislature passed an expanded domestic partnership bill, A.B. 205, extending nearly all the legal rights of married couples to people in same-sex partnerships. This effectively transformed California domestic partnerships into civil unions. Signed by Governor Gray Davis on September 19, 2003, the bill went into effect on January 1, 2005. [1] New Jersey passed such a bill on January 8, 2004. [2] Maine's legislature and governor approved a domestic partnership law in April of 2004.