In this paper, I will analyse the relation between a sense of agency and free will. It is often proposed that by investigating the former, we can find a way of judging when an action is voluntary. Haggard seems to be one of the authors believing so. To answer if this assumption is correct, I will: 1) analyse the categories of free will and agency; 2) define the sense of agency; 3) describe ways of investigating the sense of agency; 4) describe models of emergence of the sense of agency; 5) analyse the relation between agency and responsibility. I will end by discussing the actual possibility of using the sense of agency measurements (as described in experimental sciences) as markers of free will.