There are two kinds of Nuptial Agreements:
Prenuptial Agreements are made prior to any marriage vows. These agreements layout where assets go in case the marriage does not work out. Typically, both parties will need an attorney to negotiate and settle the prenuptial agreement.
Postnuptial Agreements are made during the marriage and in contemplation of divorce.
These are contracts to settle property issues in case of a divorce;
These require full disclosure of assets;
Today, the courts are inclined to enforce these agreements, if fair;
They are often very complex and require very careful drafting in order to be fair and enforcible. Both parties need an attorney.