This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book nurtures a debate that challenges the assumption that more security requires less privacy, and that more surveillance necessarily implies more security. In modern societies, surveillance is progressively emerging as a key governing technique of state authorities, corporations and individuals: 'the focused, systematic and routine attention to personal details for purposes of influence, management, protection or direction'. The underlying rationale supporting data-driven security practice is that the harvesting of personal and meta-data would permit authorities to intervene in a targeted and intelligence-led fashion: focusing their attention and their resources on emerging threats and possibly disrupting them before their occurrence. Three FP7 Security Research projects (PRISMS, PACT and SurPRISE) have addressed these and related questions. The main aims of the projects were to better understand the relation between surveillance, security and privacy, to inform policy-making and to support decision making.