This paper provides first of all the introduction to this special issue on 'Legal constraints on the indeterminate control of "dangerous" sex offenders in the community: A European comparative and human rights perspective'. The issue is the outcome of a study that aims at finding the way legal control can not only be an instrument but also be a controller of social control. It is explained what social control is and how the concept of moral panic plays a part in the fact that sex offenders seem to be the folk devils of our time and subsequently pre-eminently the target group of social control at its strongest. Further elaboration of the methodology reveals why focussing on post-sentence (indeterminate) supervision is relevant, as there are hardly any legal constraints in place in comparison with measures of preventive detention. Therefore, a comparative approach within Europe is taken on the basis of country reports from England and Wales, France, Germany, The Netherlands and Spain. In the second part of the paper, the comparative analysis is presented. Similar shifts in attitudes towards sex offenders have led to legislation concerning frameworks of supervision in all countries but in different ways. Legal constraints on these frameworks are searched for in legal (sentencing) theory, the principles of proportionality and least intrusive means, and human rights, mainly as provided in the European Convention on Human Rights to which all the studied countries are subject. Finally, it is discussed what legal constraints on the control of sex offenders in the community are (to be) in place in European jurisdictions, based on the analysis of commonalities and differences found in the comparison.