Introduction Virtually every summer Olympics since 1972 has either experienced terrorist attacks or else has been the target for terrorist plots. The terrorist groups behind these plots and attacks have come from a wide range of backgrounds, with different ideologies, different aims and different histories. As already highlighted in Chapter 1 in this volume, the Olympics have been targeted by a range of nationalist separatist groups, Christian fundamentalists, Islamist extremists, militant Marxists and others. The organisations themselves have varied from fringe groups with only a handful of people involved to movements with hundreds if not thousands of active members and budgets which can run into tens of millions of pounds. States, too, have not been above targeting the Games for violence. The one thing that all of these different groups have in common is that they judged the Olympics to be an attractive and appropriate target for violence. Despite their different ideologies and different objectives, all of these groups made a decision that the Olympics was the right target for them. It would be naive in the extreme to assume that no group will be interested in attacking future Olympics – or other major sporting events – when so many groups have shown both the willingness and the capability to do just that in the past 40 years. Why such a wide variety of groups continuously target the Olympics is one of the focuses of this chapter. It examines terrorist target selection in detail, shedding light on how and why terrorist groups select some targets and ignore others. It will also explore how states attempt to block and deter terrorist attacks and how the terrorist groups themselves react to these efforts.