This book examines temporary agency work, an enterprise conducted by employment agencies, whose main economic activity consists of engaging workers with the aim of assigning them to third party user undertakings seeking to cover their needs in workforce, so as to work temporarily under those parties’ supervision and direction. In addition to interpreting the relevant national law provisions under the light of the wording and purpose of Directive 2008/104/EC, the present study examines the issues that have arisen since national legislation enacted specific conditions and restrictions to agency work with the view of protecting agency workers. One of those issues concerns the practice of unlawful assignment of workers, usually contractors, employed by a number of businesses in order to circumvent statutory protection of agency work. This book aims to highlight those unlawful forms of worker assignment to third parties and to suggest solutions that would efficiently deal with the issue.