Secondary liability, according to the general rules on liability, is based on the issue of conscientiousness, in other words whether the intermediary knew or should have known that the right was infringed through his service. In U.S. law, the secondary liability standard is a result of case law. This paper presents the evolution of case law regarding the interpretation of secondary liability standard in U.S. trademark law. This standard was announced by the U.S. Supreme Court in Inwood Laboratories Inc. v. Ives Laboratories Inc. regarding the liability of manufacturers and distributors. In the decades that followed, the U.S. Courts, with their creative interpretations, extended the scope of application of this standard, first to intermediary market operators, and later to online service providers (internet intermediaries). Also, the development of digital technology has influenced the case law to adapt the secondary liability standard for trademark infringement to the new circumstances in the digital environment. The most significant cases in this context are Hard Rock Café Licensing v. Concession Services, Inc., Tiffany Inc. v. eBay Inc. and Rosetta Stone Ltd. v. Google Inc. Finally, 1-800 Contacts, Inc. v. Lens.com, Inc. demonstrates a slight turn of the U.S. Courts' practices towards a more flexible interpretation of secondary liability standard to online service providers.