This book explores citizens' perceptions and experiences of security threats in contemporary Britain, based on twenty focus groups and a large sample survey conducted between April and September 2012. The data is used to investigate the extent to which a diverse public shares government framings of the most pressing security threats, to assess the origins of perceptions of security threats, to investigate what makes some people feel more threatened than others, to examine the effects of threats on other areas of politics and to evaluate the effectiveness of government messages about security threats. We demonstrate widespread heterogeneity in perceptions of issues as security threats and in their origins, with implications for the extent to which shared understandings of threats are an attainable goal. While this study focuses on the British case, it seeks to make broader theoretical and methodological contributions to Political Science, International Relations, Political Psychology, and Security Studies.