An adult adoption occurs when one adult adopts another. Once an adult adoption is complete, the parties have a legal parent-child relationship with all associated rights and responsibilities. The most common reason to adopt an adult is for inheritance purposes. The second reason, almost as common, is to formalize an existing parent/child relationship, such as adopting a now adult foster child or step-child or a father who finds children they didn't know they had. Finally, adult adoptions often occur to provide perpetual care for an adult who has a diminished capacity or disability. Through the adoption process, one adult can become the responsible party and decision-maker for another adult's care.

An adult adoption proceeds under the same rules and statutes as an independent/private adoption. Meaning, the adult adoptee must give their written consent, or the legal guardian of a disabled adult adoptee must give their consent, as well as the spouse of the petitioner or the spouse's legal guardian if they are disabled.