Several branches of the U.S. Government play a role in international adoptions:
Formerly known and INS and BCIS, this federal government agency plays a large part in the international adoption process. If the USCIS doesn't give its approval to the petition to adopt, an international adoption cannot go forward. Fortunately, their Web site has detailed information about the process and free forms to download.
More Information: The USCIS and International Adoption
The State Department is the top level federal agency that oversees international procedures, including adoption. The Office of Children's Issues formulates, develops and coordinates policies and programs and provides direction to foreign service posts on international adoption, and coordinates policy and provides information on international adoption to the public. It does not get directly involved as a party to an adoption or have input into approvals and visas. The State Department plays an instrumental role in implementation of the Hague Convention on Intercountry adoption, and is the issuing authority for U.S. Passports.
More Information: The State Department and International Adoption
Both those who adopt internationally and domestically can take advantage of the Adoption Tax Credit. The difference for international adoptions is that the credit cannot be claimed before the adoption is final, so if you need to go through an adoption or re-adoption process in the States, be sure to do it quickly so you can file in time.
More Information: The IRS and International Adoption
This is the organization that tracks health problems around the world, provides information on immunizations required for travelers, and also follows procedures required for international adoptions, including the child's medical exam before coming to the U.S.
More Information: The CDC and International Adoption