Abstract: Amici take no position on whether BOOKING.COM is generic, but write to encourage the Court to be cautious in resolving this case, which involves a generic term combined with a common top-level domain name identifier (.com). Trademark applications raise almost infinitely varied scenarios, including generic terms combined with other elements, and the top-level domain name identifier has some specific features that make it analogous to functional matter. Whatever rule the Court adopts should be highly attentive to the risks to competition of overassertion of registered marks that are largely or entirely comprised of generic elements. Because courts deciding infringement cases are often unfamiliar with the context of a trademark registration, they may miss limitations on the scope of the registered mark that the Trademark Office believed existed and, as a result, enforce broader rights than the registrants should actually have. Ordinary businesses receiving cease and desist letters are even more unlikely to have the expertise to understand the limits on a registration. This practical reality should guide the Court’s standards for registrations with generic components. Relatedly, the Court should reaffirm the basic principle that “de facto secondary meaning” does not give rise to protectability as a trademark. Courts have long distinguished between “de facto secondary meaning” and secondary meaning “to which courts will attach legal consequences.” De facto secondary meaning refers to an association between a generic term and a particular producer that is usually the result of an extended period of market dominance, whether achieved through advertising or through lack of competition. Because of the need to protect potential and future competition, a generic term cannot be appropriated as a trademark even if it has de facto secondary meaning The practical exclusivity afforded by domain name registration means that there may often be de facto secondary meaning in domain names, which can be difficult to distinguish from true trademark secondary meaning. This easily elided distinction affects how the Court should evaluate Booking.com’s survey, which purports to show secondary meaning. But the fact that de facto secondary meaning does not lead to trademark status does not mean it is irrelevant to the law. Even when a term is not protectable as a trademark, narrower unfair competition remedies may be available to prevent true passing off. When a term is generic or a product shape is functional, neither can be protected as a trademark and others may not be enjoined from competing using the term or shape.. Those competitors, however, may be required to distinguish themselves in the market by adding identifiers or otherwise differentiating their use, if the competitors’ use might deceive consumers. Thus, a rule that strongly protects competition by denying registration to generic terms does not leave consumers exposed to clever bad actors.