When two people decide to get married, they're probably not thinking about the possibility of divorce. But that's exactly what comes into discussion during a prenuptial agreement or, as it's perhaps more commonly known, a prenup. A prenup is designed to pre-negotiate terms and protect the division of marital property. That includes money, of course, as well as items of value that may not be worth a lot in terms of finances; say, for example, a family heirloom — or even your pet.