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 Vermont, which is not a community property state but rather an 'equitable distribution' state, marital property is not automatically considered to be owned jointly by both spouses. Instead, during a divorce, marital property is divided in a manner that is equitable, but not necessarily equal. A marital property partition agreement, known in Vermont as a postnuptial agreement, is a legal tool that allows married spouses to alter the default rules of property division by mutually agreeing to assign certain marital assets as the separate property of one spouse. These agreements must be in writing and are subject to certain legal requirements to ensure fairness and voluntariness, including full disclosure of assets and independent legal advice for both parties. If spouses cannot agree on the division of property, a court may partition the property in a lawsuit, taking into account factors such as the length of the marriage, the contribution of each spouse to the acquisition of the marital property, and the economic circumstances of each spouse. It's important to note that Vermont's laws on postnuptial agreements and property division are found in the Vermont Statutes, particularly within titles relating to domestic relations and property.