This chapter takes a comparative state-centric approach to illustrate the core issues of defence in Europe. The chapter reviews the influence of history, size, and geography on defence in Europe. It assesses the external threats facing European countries, including territorial threats from neighbouring countries such as Russia, energy security, and cyber security, and the ways in which these threats are perceived in Europe and in European states. It then shows how states respond to these threats, examining differences between European countries in terms of their strategic culture, defence capabilities, and military alliances. Efforts to build defence cooperation between countries are examined, including NATO and the emergence of common defence policies at the EU level.