An "other transaction" (OT) is a special vehicle used by federal agencies for obtaining or advancing research and development (R&D) or prototypes. An OT is not a contract, grant or co-operative agreement, and there is no statutory or regulatory definition of "other transaction". Only those agencies that have been provided OT authority may engage in other transaction. Generally, the reason for OT authority is that the government needs to obtain leading edge R&D and prototypes from commercial sources, but some companies are unwilling or unable to comply with the government's procurement regulations. This book examines the "other transaction authority" and its uses by the federal agencies.