The California Uniform Premarital Agreement Act requires that premarital agreements be in writing and signed by both parties.   In order to be valid, the agreement must be made voluntarily by both parties and not be unconscionable. Both parties must provide fair and reasonable disclosure of their property and financial obligations to the other party. The agreement becomes effective once the parties are legally married. California state law is specific as to the matters which may be included in the agreement.  A premarital agreement may be amended once the parties are married if both parties agree to the amendment in writing.