A marital property partition agreement—also known as a partition and exchange agreement, a postmarital agreement, or a postnuptial agreement—is an agreement between spouses during marriage to convert marital property (also known as community property in some states) to one spouse’s separate property.

Property that is jointly owned by spouses or domestic partners (often owned as joint tenants with a right of survivorship) may also be partitioned or divided in a lawsuit or court action rather than by agreement of the spouses.

Laws regarding marital property partition agreements vary from state to state and are generally located in a state’s statutes—often in the family code or domestic relations code.

In California, marital property partition agreements, also known as postnuptial agreements, are recognized and enforceable. These agreements allow married spouses to alter the character of their property from community to separate property. California is a community property state, meaning that generally, all property acquired during the marriage is considered owned equally by both spouses. However, through a marital property partition agreement, spouses can agree to change the nature of specific assets or future earnings from community to separate property. Such agreements must be in writing, signed by both parties, and entered into voluntarily after full disclosure of the financial situation of both spouses. The agreement cannot be unconscionable when executed, and both parties should ideally have independent legal counsel to avoid issues of unfairness or duress. If spouses decide to partition or divide jointly owned property without an agreement, they may do so through a court action, which typically involves filing a lawsuit for partition. The court will then order the division of the property according to the principles of equity and fairness.