When we consent to something (e.g. a medical procedure, sex, a tattoo), we permit people to act in ways that would otherwise be legally or morally impermissible. However, in order for consent to be valid, certain conditions must be met. In this thesis, I discuss the condition that consent needs to be voluntary, I focus specifically on consent to medical procedures, and I argue that such consent is voluntary unless it is motivated by an influence that cannot be interpersonally justified. I call my view Interpersonal Consenter-Consentee Justification (ICCJ). ICCJ introduces the concept of interpersonal justification, known from the debate on contractualism, to the debate on consent and most clearly differs from other views in the literature by (i) focusing on the reasons or motivation for which a person consents, instead of mere causal links or counterfactuals, (ii) allowing the moral legitimacy and not just the strength of an influence to have a bearing on the voluntariness of consent, and (iii) making the behaviour of the person receiving consent (the consentee) central to its approach.