This chapter examines the Copenhagen School and its securitization model. The Copenhagen School broadens the definition of security by encompassing five different sectors: military, political, societal, economic, and environmental security. It first provides an overview of the Copenhagen School’s securitization model before discussing its application to empirical research as well as the limitations of the securitization model. It then considers the role of the securitizing actor and the importance of the ‘speech act’ in convincing a specific audience of a threat’s existential nature. It argues that the Copenhagen School allows for non-military matters to be included in Security Studies while still offering a coherent understanding of the concept of security. It also describes the dangers and the negative connotations of securitizing an issue and concludes with some cases of securitization, including the securitization of undocumented migration, securitization of drug trafficking, and the failure of securitization in the Iraq War.