Courtroom Science and Trans Youth investigates how Canadian courts engage with science and expert testimony in cases involving parental treatment of transgender youth. The book introduces the current scientific understanding of trans youth and the legal frameworks of custody and child protection in Canada. Through a critical analysis of all significant Canadian court decisions from 2000 to 2021 that address parental treatment of trans children, legal and health ethics expert Florence Ashley uncovers recurring patterns and themes in judicial reasoning. The analysis reveals that while scientific evidence can sometimes support trans youth’s identities, it often reinforces clinicians’ authority and pathologizes trans experiences, limiting young people’s autonomy. Judges frequently rely on medical expertise that may be biased or outdated, resulting in decisions that both affirm and undermine trans youth. Drawing on these findings, Courtroom Science and Trans Youth advocates for legal reform that centres the rights and voices of trans youth themselves, moving away from requiring them to “prove” their gender and towards recognizing their right to gender self-determination.