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 Colorado, which is not a community property state but rather an equitable distribution state, marital property is not automatically considered to be owned jointly by the spouses. Instead, during a divorce, marital property is divided equitably, though not necessarily equally, based on a variety of factors. A marital property partition agreement, known in Colorado as a 'marital agreement' or 'postnuptial agreement,' is a legal document where spouses can agree to change the character of property from marital to separate. This agreement allows spouses to determine how their property will be divided in the event of a divorce or death. Colorado Revised Statutes Title 14 (Domestic Matters) provides the legal framework for these agreements. To be enforceable, the agreement must be in writing and signed by both parties. Full disclosure of assets is typically required, and both parties should have the opportunity to seek independent legal advice from an attorney. If a couple does not have a marital property partition agreement and cannot agree on the division of property, a court may divide the property for them, taking into account factors such as the contribution of each spouse to the acquisition of the marital property, the value of the property set apart to each spouse, and the economic circumstances of each spouse at the time the division of property becomes effective.