21 General introduction 1 aetiology of gender dysphoria, the boundaries of medicine, and the concepts gender, child competence, and best interests are described. It examines whether moral intuitions, ideas, and theories of people who criticize the use of PS differ from those of people who support it, and in what sense. The considerations of 36 professionals of 17 treatment teams from 10 different countries were taken into account while using individual semi-structured interviews and open-ended questionnaires. To do justice to the adolescents’ developing autonomy to make medical decisions, especially when it concerns profound treatments such as PS, serious consideration to the opinions of transgender adolescents needs to be given. Insight into the way these adolescents perceive the concepts sex and gender, and the use of PS in the context of gender dysphoria will help to adequately support these adolescents in their decisionmaking process regarding this treatment and give them the care they need. Chapter 3 therefore explores the adolescents´ considerations regarding the use of PS, and regarding the concepts sex and gender. Furthermore, it describes whether these considerations differ from those of clinicians working in gender treatment teams and of people who are critical about the use of PS in gender dysphoria, and if so, in what sense. To gain this insight semi-structured interviews with 13 adolescents concerning the use of PS were conducted in the Netherlands. Eight transgender adolescents who proceeded with GAMT after PS, and five adolescents who discontinued PS (aged 13-18 years) were interviewed. Part 2 discusses the minors’ medical decision-making competence (MDC) regarding starting PS treatment. Competence is an important topic in the controversies surrounding the use of PS. There is discussion whether transgender adolescents are competent to give informed consent to start this treatment. In some countries, this doubt has even led to limited access to this treatment. We therefore examine the MDC concerning PS of transgender adolescents. To assess MDC, judgements based on the reference standard (clinical assessment) and the MacArthur Competence Assessment Tool for Treatment (MacCAT-T), a validated semi-structured interview, were used. In addition, potential associated variables on MDC, such as age, intelligence, sex, and psychological functioning, were investigated. Chapter 4 describes the cross-sectional semi-structured interview study with 74 transgender adolescents (aged 10-18 years; 16 birth-assigned boys, 58 birthassigned girls) within two Dutch gender identity clinics we performed. Chapter 5 explores the perceptions concerningMDC to start PS treatment for eight transgender adolescents who proceeded with GAMT after PS, six adolescents who discontinued treatment with PS, 12 of their parents, and 10 clinicians working in gender treatment teams. For this study individual semi-structured interviews and focus groups were used. Knowing what the perspectives of the adolescents, their parents, and clinicians are regarding the adolescents’ MDC will increase our understanding of the decision-making process.