My thesis will basically be focusing on the one part of the freedom unit in EU, which is free movement of person, particularly the free movement of workers. I deal with how this basic right evolves, what kind of legal source regulate it, in which cases can the Member States restrict it, while making a short reference to several related themes: students, lawyers, and social advantages. To understand the free movement in theory and practice we have to examine the related case-law of the European Court of Justice, what has played an essential role in the determination of the subjects of free movement, by shifting its focus continuously from the free movement of workers to the free movement of persons.