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 Minnesota, which is not a community property state but rather an 'equitable distribution' state, marital property is divided equitably in the event of a divorce, rather than strictly equally. A marital property partition agreement, known in Minnesota as a postnuptial agreement, allows married spouses to agree on the division of their property during the marriage. These agreements can be used to convert marital property into the separate property of one spouse. Under Minnesota law, specifically Minnesota Statutes Section 519.11, postnuptial agreements must be in writing, made in good faith, and executed with the voluntary and full disclosure of each party's financial situation. Both parties must also have the opportunity to consult with an attorney of their choosing. For a postnuptial agreement to be enforceable, it must not be unconscionable at the time of enforcement. If spouses cannot agree on the division of property, the courts will intervene and divide the property equitably based on a number of factors, including the length of the marriage, the financial situation of each spouse, and contributions to marital property, among others. It is important for individuals considering a postnuptial agreement to consult with an attorney to ensure that the agreement is properly drafted and enforceable under Minnesota law.