This chapter examines socio-legal research and qualitative empirical studies, and discusses the contradictory ‘broad’ and ‘narrow’ notions of ‘posting of workers’. It explores the key argument for distinguishing posting in the framework of free service provision from free movement of migrant labour is based on the fictitious legal presumption that posted workers do not enter the labour market of host states. When transition periods concerning Article 45 TFEU ended, posting remained attractive as a tool for cheaper labour recruitment, compared to the free movement of workers, since Article 45 TFEU prescribes full equal treatment of workers, including remuneration and all other labour standards and social advantages. As a consequence of the Rush Portuguesa judgement, prohibition of discrimination on the grounds of nationality, enshrined in the acquis on the free movement of workers concerning pay and other working conditions, was rendered inoperative for posted workers. The broad notion takes into account irregular posting and unreported or fraudulent forms of labour mobility.