Thousands of people have died at the hands of terrorist groups who rely on state support for their activities. Iran and Syria are well known as sponsors of terrorism, while other countries, some with strong connections to the West, have enabled terrorist activity by turning a blind eye. Daniel Byman's hard-hitting and articulate book analyzes this phenomenon. Focusing primarily on sponsors from the Middle East and South Asia, it examines the different types of support that states provide, their motivations, and the impact of such sponsorship. The book also considers regimes that allow terrorists to raise money and recruit without providing active support. The experiences of Iran, Pakistan, Afghanistan, Syria, Saudi Arabia, and Libya are detailed here, alongside the histories of radical groups such as al-Qaida and Hizballah. The book concludes by assessing why it is often difficult to force sponsors to cut ties to terrorist groups and suggesting ways in which it could be done better in the future.