Security measures take up more and more space in our cities. In parallel, the security industry is growing. To understand these developments, we must take a step back and unfold the rationales and theories that lie behind such security measures and their materiality, specifically in the security industry. This article uses the case of the newly developed counterterrorism industry in Copenhagen to unpack some of the general dynamics that enable growth in the security industry and an increase in security measures. Building on ethnographic fieldwork among security companies, architecture firms, the Municipality
of Copenhagen, the national security service, and others, this article shows how theories about counterterrorism develop in an interplay between this diverse group of security actors. The article zooms in on a security company and an architecture firm, and their divergent approaches to counterterrorism measures, and shows how both develop in conflict with local city values and security-skeptical actors. The two companies work hard to establish and promote theories not only about counterterrorism but also about what is best for the city and its citizens, which help legitimize their work in Copenhagen and shape public opinion on counterterrorism, and, ultimately, the materiality of the city