What can and can't be protected by a prenup?

In California, a prenup can define what is considered separate property and what is community property (marital property) during marriage, in the event of a divorce, and upon death. It can specify the choice of law that will apply if you divorce and address how funds will be used during the marriage, such as payments from community funds towards someone's separate property residence. You can also place limits on spousal support within a prenup. Additionally, a prenup can outline how assets will be distributed upon death, if you wish to change the default legal provisions. 

A prenup cannot include anything illegal or unenforceable, such as decisions regarding child custody, child support, or the impact of infidelity.