15 U.S.C. §1060(a)

1. (1) A registered mark or a mark for which an application to register has been filed shall be assignable with the good will of the business in which the mark is used, or with that part of the good will of the business connected with the use of and symbolized by the mark. Notwithstanding the preceding sentence, no application to register a mark under section 1(b) shall be assignable prior to the filing of an amendment under section 1(c) to bring the application into conformity with section 1(a) or the filing of the verified statement of use under section 1(d), except for an assignment to a successor to the business of the applicant, or portion thereof, to which the mark pertains, if that business is ongoing and existing.
2. (2) In any assignment authorized by this section, it shall not be necessary to include the good will of the business connected with the use of and symbolized by any other mark used in the business or by the name or style under which the business is conducted.
3. (3) Assignments shall be by instruments in writing duly executed…

37 C.F.R. §3.1 (Extract)

*** Assignment means a transfer by a party of all or part of its right, title and interest in a patent, patent application, registered mark or a mark for which an application to register has been filed.

In an application under §1(b) of the Trademark Act, 15 U.S.C. §1051(b), the applicant cannot assign the application before the applicant files an allegation of use (i.e., either an amendment to allege use under 15 U.S.C. §1051(c) or a statement of use under 15 U.S.C. §1051(d) ), except to a successor to the applicant’s business, or portion of the business to which the mark pertains, if that business is ongoing and existing. Section 10 of the Trademark Act, 15 U.S.C. §1060; 37 C.F.R. §3.16.

The primary purpose of this provision is to ensure that a mark may only be assigned along with some business or good will, and to prevent "trafficking" in marks.

As a general rule, the United States Patent and Trademark Office ("USPTO") does not investigate or evaluate the validity of assignments. Therefore, the examining attorney must issue an inquiry concerning the compliance of an assignment with the cited provisions of §10 only if:

1. (1) The application itself includes a statement indicating that the assignee is not a successor to the original applicant’s business, or portion of the business to which the mark pertains, if that business is ongoing and existing; or
2. (2) All of the following conditions are present:
   1. (a) The assignment is executed before the filing of an allegation of use;
   2. (b) The applicant submits the assignment document for inclusion in the application record in the Trademark database, and not just to the Assignment Recordation Branch; and
   3. (c) The assignment document fails to include the relevant language from §10 to the effect that the assignment includes the entire business of the applicant/assignor or the portion of the business to which the mark pertains.

The examining attorney should not require the submission of assignment documents to determine compliance.

If the examining attorney issues an inquiry, the applicant’s statement that the assignment was in compliance with the cited provision of §10 is sufficient to resolve the issue. This statement may be entered through an examiner’s amendment.

The assignment of an intent-to-use application to someone who is not the successor to the applicant’s business before filing an allegation of use renders the application void, and any resulting registration must be cancelled. Cent. Garden & Pet Co. v. Doskocil Mfg. Co., 108 USPQ2d 1134, 1146 (TTAB 2013) ; Clorox Co. v. Chem. Bank, 40 USPQ2d 1098, 1105-06 (TTAB 1996); cf. Amazon Techs., Inc. v. Wax, 95 USPQ2d 1865, 1872 (TTAB 2010) (finding "the assignment from one joint applicant to another, where the assignee joint applicant was and remains an owner of the application is more in the nature of 'relinquishment' of ownership rights by one joint owner than a true 'assignment' to a different legal entity, and, thus, it is not prohibited under §10 of the Trademark Act").

Under §72 of the Trademark Act, 15 U.S.C. §1141l, an extension of protection to the United States may be assigned, together with the good will associated with the mark, only to a person who is a national of, is domiciled in, or has a bona fide and effective industrial or commercial establishment in a country that is party to the Madrid Protocol (or in a country that is a member of an intergovernmental organization that is a party to the Madrid Protocol). See TMEP §501.07 for further information about assignment of §66(a) applications and registered extensions of protection to the United States, and TMEP Chapter 1900 for further information about the Madrid Protocol.