The exploitation of labour is one of the most widespread forms of so-called "modern slavery" and, therefore, there is a need for an in-depth analysis in order to aid the development of a successful counter-strategy. Taking the definitions contained in international law as its starting point, this book is an investigation of the fine lines between labour exploitation, the trafficking of human beings and other phenomena such as forced labour and slavery. An analysis of the supranational framework concludes with an examination of the jurisprudence produced by the Court of Strasbourg in article 4 of the ECHR, legislation to which the theory of positive obligations elaborated by the Court was soon extended. With regard to specific nations, the book focuses on Italy, France, Spain and the UK, with an analysis of how supranational obligations to criminalize certain activities have been implemented, as well as including an evaluation of the adequacy of the incriminating provisions that have been adopted at national level in order to effectively combat the complex phenomenon of modern slavery.