This dissertation seeks to understand the interplay between informal articulations of social categories and formal instantiations of those categories in official language. Specifically, it explores the process of social categorization as it is used to identify threats to national security. The research employed a qualitative, document-based, multi-case study methodology. The cases were purposefully selected to provide a group of documents that were diverse in genre, ideological and historical nature, but were also all produced in order to identify and categorize threats to the national security of each country. The documents were analyzed using techniques from critical discourse analysis and systemic functional linguistics. It was anticipated that through this analysis, a better understanding of the way categories are used in national security to police society and to enlist citizen support for government policies could be achieved. The analysis could then be used to elucidate how the messages conveyed by government media campaigns may draw on informal or stereotypical categories that lead to profiling and xenophobia. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]