Drawing extensively on the entire body of applicable case law, this in-depth study analyses what the free movement of persons provisions of the EC Treaty have come to mean in today's Europe. The author posits the emergence of a new constitutional dimension whereby the Member States bear considerable duties towards Union citizens qua citizens rather than just qua economic actors?a duty not to interfere with individual rights, a duty to respect individual rights, and a duty to protect individual rights-duties to be understood in the context of Union citizenship.