Contract entered into by a couple prior to marriage or a civil union that enables them to select and control many of the legal rights they acquire upon marrying, and what happens when their marriage eventually ends by death or divorce. Laws vary between both states and countries in both what content they may contain and under what conditions and circumstances that a prenuptial agreement may be declared unenforceable, such as an agreement signed under fraud, duress or without adequate disclosure of assets.

A marriage agreements may limit the parties' property and spousal support rights, but also to guarantee either party the right to seek or receive spousal support up to a certain limit. It may be impossible to set aside a properly drafted and executed prenup. A prenup can dictate not only what happens if the parties divorce, but also what happens when they die. They can act as a contract to make a will and/or eliminate all of one's rights to property, probate homestead, probate allowance, right to take as a predetermined heir, and the right to act as an executor and administrator of one's spouse's estate.

Unlike all other contract law, consideration is not required, although a minority of courts point to the marriage itself as the consideration. Through a prenup, a spouse can completely waive rights to property, alimony or inheritance as well as the elective share and get nothing in return. Choice of law provisions are critical in prenups. Parties to the agreement can elect to have the law of the state they are married in govern both the interpretation of the agreement and how property is divided at the time of divorce. In the absence of a choice of law clause it is the law of the place the parties divorce, not the law of the state they were married that decides property and support issues.