This dissertation highlights the role of the Working Group on Arbitrary Detention, as an evidence of the evolution of the mechanisms of control at the level of the Commission on Human Rights. Throughout time, extra-conventional mechanisms at the disposal of the Commission on Human Rights have undergone a remarkable evolution. In this context, thematic mechanisms gathered momentum, among which the Working Group on Arbitrary Detention -created in 1991- stands out. This group focuses on the investigation of the arbitrary character of detentions imposed on specific individuals, applying to any member of the United Nations, even those that are not party to treaties or conventions. It acts, as well, protected from political pressures, only based on the expertise of its five expert-members to present its opinions. Given the objectivity and non-selectivity of its performance and considering its capacity of effectively protecting specific individuals, the Working Group on Arbitrary Detention represents a worthy instrument of investigation and control in the hands of the Commission.