22 Chapter 1 Part 3 describes the significance of starting treatment with PS or refraining from the treatment, and the use of fertility preservation. Treatment with PS for transgender adolescents was developed, among others, to extent the exploration and assessment phase by providing the adolescents more time to consider their gender, the diagnosis gender dysphoria, and the potential use of GAH, without the distress associated with endogenous pubertal development. Chapter 6 describes the minors’ trajectories after the initiation of treatment with PS, and reports the reasons for extended use and discontinuation of treatment with PS in order to find out whether PS is indeed being used as a phase to further explore and assess. Chapter 7 focuses on how PS is perceived by transgender adolescents, their parents, and clinicians. Despite PS being the current first choice treatment, little research had examined the functions of PS from the perspectives of transgender adolescents, their parents, and clinicians. Knowledge about the perceived functions of PS can help to adequately support these adolescents in their decision-making process and give them the care they need. Chapter 7 describes the outcomes of our study using individual semi-structured interviews and focus groups to obtain insight in the perspectives of eight transgender adolescents who proceeded with GAMT after PS, six adolescents who discontinued treatment with PS, 12 of their parents, and 10 clinicians regarding the functions of PS. One major concern regarding starting treatment with PS for transgender minors entails the consequences for the minors’ fertility. As far as currently known, the effects of treatment with PS on the secondary sex characteristics’ development and the gonadal function are reversible when the treatment is discontinued. However, transgender minors who start treatment with PS at a young age, and subsequently start treatment with GAH and undergo gonadectomy, cannot make use of fertility preservation since they never undergo their endogenous puberty. In order to get more insight in this currently one of the most challenging topics concerning medical treatment for transgender adolescents, chapter 8 reports the rate of fertility preservation among a cohort of Dutch transgirls who started treatment with PS. Furthermore, the reasons why these adolescents did or did not make use of fertility preservation are described. As has become clear of the above, clinicians frequently face ethical dilemmas arising from the care they provide. Part 4 describes the use of clinical ethics support for clinicians who are involved in (medical) care for transgender children and adolescents, in order to support these clinicians in dealing with these challenges more effectively. The research discussed in chapter 9 describes the treatment teams’ perceived value and effectiveness