Private security companies (PSCs) can help to enhance security but may also contribute to more insecurity. Their activities can also have positive or negative effects on individuals’ human rights. But when and how should one hold PSCs accountable for the impacts they generate? And what are the responsibilities of states that privatise security? Who will control that this privatisation does not happen to the detriment of the wider public? Whose Responsibility? Is a collection of papers presented and discussed at a meeting of Southeast European private security experts in December 2016 and answers many of the questions surrounding responsibility and accountability in the private security sector.