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 Indiana, which is not a community property state but 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 Indiana as a postnuptial agreement, allows spouses to agree on how their property should be classified and divided. This agreement can be used to convert marital property into the separate property of one spouse. For such an agreement to be valid, it must be in writing and signed by both parties. It is also important that both parties disclose their assets fully and that the agreement is executed without coercion or fraud. Indiana courts will generally uphold a postnuptial agreement if it meets these criteria. However, if spouses cannot agree on the division of property, a court will decide based on what is equitable, considering factors such as the length of the marriage, the income and earning potential of each spouse, and contributions to marital assets. It's important to consult with an attorney to ensure that a postnuptial agreement is properly drafted and meets all legal requirements.