A Prenuptial Agreement is executed prior to marriage and a Postnuptial Agreement is executed after a marriage takes place. If your family is the result of multiple marriages or prior relationships, a Prenuptial or Postnuptial Agreement can be an effective estate planning tool to ensure that children from different marriages or relationships will be treated in the manner that you wish. With a Prenuptial or Postnuptial Agreement, you can determine what goes to your current spouse and what goes to your children from a prior relationship.