A trademark is a word, mark, symbol, or phrase that is used to identify a seller's product and distinguish it from other's products. Trademarks are protected primarily by federal law (although some state actions regarding trademarks are still available). The primary federal statute, the Lanham Act, was enacted in 1946 and is codified as amended in several sections of Title 15 of the United States Code. Trademark registrations are granted by the United States Patent and Trademark Office (USPTO).
Secondary sources can give you an overview of the application of the law, some history, citations to primary sources, and analysis on unsettled points of law. Treatises can be an especially good choice for trademark law research because it is an area of primarily statutory law of national importance that is closely tracked by treatise authors. The following treatises are generally regarding as the leading authorities:
Deskbooks and practice guides are another good place to start your research, especially if you are unfamiliar with Trademark Law and need a straightforward introduction. These tools can also be especially helpful for understanding how to address practical issues such as prosecuting a trademark, researching a mark's history, or handling cease and desist letters.
At the federal level, trademarks are registered with the USPTO. Among other things, the USPTO reviews applications and accompanying materials (all applications require some representation of the mark) and assesses the applications's compatibility with federal trademark law and USPTO classification guidelines