37 CFR § 1.413 - The United States International Searching Authority.
(a) Pursuant to appointment by the Assembly, the United States Patent and Trademark Office will act as an International Searching Authority for international applications filed in the United States Receiving Office and in other Receiving Offices as may be agreed upon by the Director, in accordance with the agreement between the Patent and Trademark Office and the International Bureau (PCT Art. 16(3)(b)).
(b) The Patent and Trademark Office, when acting as an International Searching Authority, will be identified by the full title “United States International Searching Authority” or by the abbreviation “ISA/US.”
(c) The major functions of the International Searching Authority include:
(1) Approving or establishing the title and abstract;
(2) Considering the matter of unity of invention;
(3) Conducting international and international-type searches and preparing international and international-type search reports (PCT Art. 15, 17 and 18, and PCT Rules 25, 33 to 45 and 47), and issuing declarations that no international search report will be established (PCT Article 17(2)(a));
(4) Preparing written opinions of the International Searching Authority in accordance with PCT Rule 43bis (when necessary); and
(5) Transmitting the international search report and the written opinion of the International Searching Authority to the applicant and the International Bureau.