A prenuptial agreement is a legal contract prepared, negotiated and executed by all parties prior to their marriage. A prenuptial agreement must be in writing and executed only after the parties have exchanged full and frank financial disclosure. The purpose of a prenuptial agreement is to define each parties' rights and obligations in the event of a divorce. Each party to a Florida prenuptial agreement should ideally have the advice of an experienced family law attorney. A prenuptial agreement may not establish custody, timesharing and parental responsibility. A postnuptial agreement is similar to a prenuptial agreement except is completed after the parties are married.