In the United Kingdom (UK), private security contractors are taking on increasingly prominent roles, their market failures are becoming ever more controversial, and the public regulator responsible for controlling their activities -the Security Industry Authority (SIA) -is undergoing major restructuring. Now is therefore a good time to refl ect on the successes, failures and prospects of UK security regulation. With this in mind, the article advances an up-to-date and comprehensive evaluation of the SIA ' s regulatory practices. Its headline fi ndings are twofold. First, the picture is mixed: the SIA has succeeded in meeting its two core regulatory objectivesto reduce criminality and to raise standards -but only to a degree. Second, context matters: in order to understand SIA ' s performance, it is necessary to interpret its activities within the broader UK regulatory environment, in particular, the Better Regulation agenda.