Contrary to the cliche, spouses don't always share everything in their lives. Even in a community property state, where your spouse is normally co-owner of whatever you earn or acquire in marriage, he may have no right to money or assets you inherit. A lot depends on how you manage your inheritance.
Any property you inherit before you tie the knot is yours alone. The same is true for a post-wedding inheritance if you're the one named in the will. If someone leaves property in both your names, your spouse is co-owner even if you were closer to the deceased. For example, even if you are certain that your late father wouldn't want any of his assets to go to your spouse if you divorce, your opinion can't change a written will.
Your inheritance won't remain yours alone if you don't treat it like separate property. If you and your spouse have a joint account, for instance, depositing inherited money there indicates you're willing to share it with your spouse. The same is true if you inherit a house and put both your names on the deed. Spending your spouse's money to manage an inherited business is another sign you consider him an equal owner.
If you want your inheritance separate from your spouse's finances, you can handle the inheritance in a way that shows this. When you inherit cash, put it in a separate account; when it's property, keep the title in your name. Don't spend the cash on marital bills as you do your salary. A prenuptial or postnuptial agreement that specifically protects possible inheritances is the strongest step you can take to guarantee that your spouse has no claim to your inheritance.
If you keep your inheritance separate, the judge usually lets you keep it in a divorce. There are exceptions, such as if your ex-to-be needs money for heavy medical expenses. A prenup can only protect you if it's in writing -- a verbal agreement won't cut it -- and if it conforms to your state's laws. It also has to be fair: If you pressure your spouse to sign it without reading it, for instance, a judge may decide to override it.