In recent years, as well explained by Annette Kur,1 an assessment of the function of trademarks has become a direct doctrinal mechanism used by courts in the European Union to determine the scope of trademark protection in a number of contexts. In the United States, no equivalent doctrinal mechanism has developed, at least not in those precise terms; US courts do not speak the language of “functions” as the Court of Justice has now done for two decades. However, features of US trademark law have clearly been shaped with a similar awareness of the importance of the functions of marks. In particular, US courts have for over a century referenced the core function of a trademark to identify the source or origin of the product on which it is affixed. And litigants and scholars seeking to expand the scope of protection have sought to emphasize that marks do much more than identify source, often tendering explanations that hint at the advertising and investment functions of marks (without using those terms).