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 New Mexico, which is a community property state, a marital property partition agreement, also known as a postnuptial agreement, allows married spouses to change the character of their property from community to separate property. This type of agreement must be in writing and signed by both parties. It is typically used to establish financial rights and responsibilities during the marriage and can also address how property will be divided in the event of a divorce or death of one of the spouses. New Mexico law requires that such agreements be entered into voluntarily and with full disclosure of assets by both parties. The agreement must also be fair and not unconscionable at the time of signing. If spouses decide to partition or divide jointly owned property through a lawsuit or court action, this process is governed by New Mexico's statutes and case law, which provide the legal framework for property division upon divorce or legal separation. It is important for individuals considering a marital property partition agreement in New Mexico to consult with an attorney to ensure that the agreement complies with state law and adequately protects their interests.