This report analyses the socio-economic and political forces that create and maintain the presence of undocumented migrant workers in Europe. It provides the backdrop for considering what rights should be granted to undocumented migrant workers. The situation in various economic sectors in Europe is analysed, and issues such as the protection of victims of forced labor and the problems associated with regularization campaigns are presented. The report highlights the role played by social inspectors, trade unions and NGOs in protecting undocumented migrant workers, and offers recommendations for specific policy measures.