From fears of anarchist terrorists in the early twentieth century through cold war conflict and contemporary fears of extremist religious terrorists, the American library community responded to the use of libraries as a site for surveillance and source of dangerous information in an increasingly proactive and organized manner. This paper traces the evolution of privacy norms and standards within the American library profession, focusing on the lack of regard for patron confidentiality in the early twentieth century, the development of privacy norms in the American Library Association (ALA) Code of Ethics in 1938, and the increased protection of privacy rights as the profession's conceptions of privacy formed around the ALA's codes. Using Nissenbaum's (2009) "contextual integrity" framework within a broad historical analysis of ALA publications, the paper examines the role of its codes regarding privacy in establishing a normative framework around which the continued application of privacy standards in libraries has taken place despite new technological challenges and continued pressure from governments and outside organizations to exploit patron information. The paper concludes that the ALA's unambiguous stance on, and consistent advocacy for, privacy standards across the profession has enabled reactions to violations of privacy norms that have shifted with technologies and new social pressures. The ALA's historic ability to maintain and protect these professional standards serves as a compelling model for new information professions that work to set professional standards in areas that range from data-analytics to social networking.