Adoption registries are databases handled by the state or independently that allow members of the adoption triad to show their consent for the release of their information to other searchers or their willingness to reunite with the their birth relatives.
State registries are the first place a searching adoptee or birth relative should go. These registries are dependent on mutual consent, meaning both parties will need to register with the state before identifying information is released about either party. In terms of search and reunion methods, this is one of the more passive routes.
There are registry websites, where people can register online and then search manually through the other registrants for a potential match. There are also search services that work through investigation. However, these are limited by the amount of information a searcher has on the other party. For example, it's possible to search through the Internal Revenue Service but it requires the social security number of the person in question. Obviously, if this kind of personal information was known the adoptee or birth relative wouldn't be turning to the IRS.
Another active option for searchers require them to petition the courts for an order to have a confidential intermediary facilitate communication between the adoptee and birth relative. A C.I. will have access to the adoption record and be sworn to confidentiality. Often, this avenue of contact cannot be granted until the searcher has been registered with the state for a certain time.