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 Pennsylvania, which is an equitable distribution state rather than a community property state, marital property is not automatically considered to be owned jointly by both spouses. Instead, marital property is divided equitably, but not necessarily equally, in the event of a divorce. A marital property partition agreement, known in Pennsylvania as a postnuptial agreement, allows spouses to agree on how their property should be classified (as either marital or separate property) and divided in the event of a divorce. These agreements must be in writing and are subject to certain legal requirements to be enforceable, such as full and fair disclosure of assets and voluntary execution without duress or coercion. If spouses cannot agree on the division of property, the courts will divide it in an equitable manner, considering factors such as the length of the marriage, the contributions of each spouse, and their respective economic circumstances. It's important to note that such agreements are distinct from prenuptial agreements, which are made before marriage, and from partition actions, which are court actions to divide property when spouses cannot agree. An attorney can provide guidance on drafting a postnuptial agreement that complies with Pennsylvania law.