The right to self-determination is firmly established in various national and international legal documents, as well as in declarations and codes of medical associations. Medical or research-related interventions can generally only be performed with the informed consent of the person concerned. In this chapter, we, firstly, describe the elements of informed consent and elaborate on the concept of shared decision-making and relevant aspects of the professional-patient relationship in mental healthcare. We then discuss why, what about, how, when and by whom patients with mental disorders should be informed and how decision support can be provided. We conclude by pointing out ethical conflicts which may occur in the context of informed consent, including situations in which patients lack mental capacity and, therefore, cannot give informed consent themselves.