Seabed Boundary Act - Title I - Authorizes the Attorney General, with the concurrence of the Secretaries of State, of the Interior, of Commerce, and the head of any other appropriate Federal department or agency, to agree with appropriate State officials as to the specific description of all or part of the boundary between the areas of the seabed and subsoil in which the United States and the State are respectively entitled, on the date of agreement, to control the exploration for and exploitation of the living and/or nonliving natural resources.

Title II - Prescribes a procedure by which, following an agreement, a seabed boundary may be immobilized.

Title III - Provides for waiver by a State of its right to the living and/or nonliving natural resources of the seabed or subsoil which would accrue to it as a result of changes in any portion of its coastline.

Title IV - Declares that no seabed boundary established according to this Act shall affect, determine, or prejudice the location of the territorial sea of the United States. States that seabed boundary agreements shall not determine State boundaries for any purpose except exploration and exploitation of natural resources.