This chapter analyses how terrorists and their opponents work to achieve political and military objectives. It discusses what terrorists have commonly been able to accomplish, the techniques they have commonly employed, and the resources they have commonly required. The chapter considers the methods that state governments and others have commonly used against terrorists and the strategic decisions those who fight terrorists must make. It describes how terrorists fit into broader struggles in world politics and considers the proposition that an exceptionally vicious new terrorism presents an unprecedented threat in the twenty-first century. The chapter aims to distinguishe between terrorism and insurgency. Terrorism, strictly speaking, is an indirect attempt to achieve goals by frightening others into responding in useful ways to the terrorists. Terrorists also work with superficially legitimate organisations. Charities, for instance, may provide terrorists with money, legal advice, and other forms of support. Even small states can support ambitious terrorist campaigns.