This is a wise thing to do. Typically, there are family law lawyers, and/or trusts and estates lawyers, who offer these as part of their practice. These vary by state. Usually, both spouses are required to be represented by different attorneys to protect their interests and have a full and fair disclosure of assets and what they are agreeing to settle or forego if the marriage ends. These are especially important where there are children from previous relationships/marriage(s), and their interests need to be protected. Estate planning including Trusts may also be appropriate.