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 South Dakota, marital property is not recognized as community property, as South Dakota is not a community property state. Instead, it follows the principle of equitable distribution. A marital property partition agreement in South Dakota, commonly referred to as a postnuptial agreement, allows married spouses to agree on how their marital property should be divided in the event of a divorce or death. Such agreements must be in writing and are subject to certain legal requirements to be enforceable, including full disclosure of assets and liabilities, and both parties must enter into the agreement voluntarily and without coercion. The agreement cannot be unconscionable and must not promote divorce. If spouses wish to partition or divide jointly owned property without an agreement, they would typically need to seek a court order through a divorce proceeding or a separate civil action. The relevant laws can be found in the South Dakota Codified Laws, particularly within the chapters that address domestic relations and property rights during marriage.