The Lanham (Trademark) Act (Pub.L. 79–489, 60 Stat. 427, enacted July 6, 1946, codified at 15 U.S.C. § 1051 et seq. (15 U.S.C. ch. 22)) is the primary federal trademark statute of law in the United States. The Act prohibits a number of activities, including trademark infringement, trademark dilution, and false advertising.
Named for Representative Fritz G. Lanham of Texas, the Act was passed on July 5, 1946, and signed into law by President Harry Truman, taking effect "one year from its enactment", on July 6, 1947. In rare circumstances, a conflict will arise between trademarks that have been in use since before the Lanham Act went into effect, thus requiring the courts to examine the dispute according to the trademark act that existed before the Lanham Act.
The Act has been amended several times since its enactment. In 2003, the U.S. Supreme Court ruled that the law had no impact on public domain works in Dastar Corp. v. Twentieth Century Fox Film Corp.
The Lanham Act is divided into the following four subchapters:
- Subchapter I – The Principal Register – §§ 1051–1072 (Sections 1–22)
- Subchapter II – The Supplemental Register – §§ 1091–1096 (Sections 23–28)
- Subchapter III – General Provisions – §§ 1111–1129 (Sections 29–45) [note: §§ 1128 & 1129 have no corresponding Lanham Act number]
- Subchapter IV – The Madrid Protocol – §§ 1141–1141n (not part of the original Lanham Act)
Note that there are gaps between the United States Code sections, to accommodate the insertion of new statutes into the Code. Two such additions have been made to Subchapter III, with the later creation of the National Intellectual Property Law Enforcement Coordination Council codified at 15 U.S.C. § 1128, and the passage of prohibitions against cyberpiracy originally codified at 15 U.S.C. § 1129, but now covered by 15 U.S.C. § 8131.
Subchapters I and II 
The provisions of Subchapter I set forth the right of trademark owners to attain a federal registration of their marks. Subchapter I sets forth the requirements that a mark must meet to receive a registration on the Principal Register, which bestows various rights on the trademark owner to prevent others from infringing their mark. Among the requirements are prohibitions against the registration of marks that are confusingly similar to existing marks, are generic or merely descriptive, are scandalous or immoral, or fall onto certain other prohibited categories. Subchapter I also sets forth certain procedural requirements, such as the submission of an affidavit of continued use after five years of registration.
Subchapter II sets forth a form of registration on the Supplemental Register, for certain marks that are unregistrable under Subchapter I, but may become registrable in the future, such as those that are merely descriptive. This form of registration, while not granting all the protections of registration on the Principal Register, does provide notice to potential infringers that the mark is in use, and also provides some procedural benefits.
Subchapter III 
The provisions of Subchapter III are the heart of the Lanham Act, with Sections 42 and 43 of the act setting out the remedies that can be sought when a trademark is infringed. These provisions can be used to restrict, through the use of injunctions and damages, the importation of goods that infringe or counterfeit registered trademarks.
Section 43(a) (codified at 15 USC 1125(a)) is the "likelihood of confusion" standard for infringement of an unregistered trademark or trade dress. Courts still frequently refer to this as "Section 43(a)".
Section 43(a)(1)(B) is also often used when false or misleading statements are alleged to have hurt a business. A claimant under this section must prove three things: there was a false or misleading statement made, the statement was used in commercial advertising or promotion, and the statement creates a likelihood of harm to the plaintiff.[dubious ]
Section 43(a)(1)(A) (http://www.law.cornell.edu/uscode/15/usc_sec_15_00001125----000-.html) is also often used when false or misleading statements are alleged to have hurt a consumer or business. The claimant must prove that a false or misleading statement was made in commerce and that the statement creates a likelihood of harm to the plaintiff.
Subchapter III includes the Anticybersquatting Consumer Protection Act as 1125(d). The Lanham Act has also been amended at 1114(2)(D) to incorporate provisions of the ACPA.
Although the Lanham Act sets out clear parameters as to what constitutes trademark infringement, subsequent court decisions, especially those involving the Internet, have loosened the strictures. 
See also 
- Lanham Act, § 46.
- Rothman, Jennifer E. "Initial Interest Confusion: Standing at the Crossroads of Trademark Law". ardozolawreview.
Further reading 
- Lemley, Mark A. (1999). "The Modern Lanham Act and the Death of Common Sense". Yale Law Journal (The Yale Law Journal Company, Inc.) 108 (7): 1687–1715. doi:10.2307/797447. JSTOR 797447.
- Phelps, D. M. (1949). "Certification Marks under the Lanham Act". Journal of Marketing (American Marketing Association) 13 (4): 498–505. doi:10.2307/1247789. JSTOR 1247789.