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 Kansas, 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 Kansas as a postnuptial agreement, is a legal document that spouses can enter into during marriage to designate certain marital property as separate property of one spouse. This agreement can be used to alter the default rules of property division in the event of a divorce. Such agreements must be in writing and are subject to certain legal requirements to be enforceable, including full disclosure of assets and voluntary signing without coercion. Kansas statutes do not specifically address marital property partition agreements, but they are recognized under Kansas case law as long as they meet the general requirements for contracts and do not violate public policy. If spouses cannot agree on the division of property, a court may partition the property in a lawsuit, taking into account factors such as each spouse's contribution to the property and the economic circumstances of each spouse.