Seven guiding principles for gender-responsive detention reform are outlined. The first guideline advises that adolescent girls in the justice system differ from boys developmentally in their focus on relationships; their internalized responses to trauma; and their externalized responses to trauma in the form of aggression. The second principle notes that gender-responsive policies and practices are fundamental to a constitutional and individualized juvenile justice system. Other principles advise that system leaders should examine both decisionmaking processes and attitudes toward girls in the juvenile justice system. Other advisory statements are that data collection and analysis are critical to effective detention reform for girls; intersystem collaboration is essential to addressing gender disparities; detention facility conditions should address girls’ needs and vulnerabilities; and gender-responsive strategies should be based on strengths not deficits. In comparing the needs of girls in detention with the conditions of detention, this booklet concludes that detention conditions exacerbate physical health and mental health conditions of girls. Adequate mental health screening is not common, nor is mental health treatment; and temporary detention disrupts community mental health treatment as well as treatment through medication. Another deficiency of detention for girls is inadequate education. The quality of education in secure detention is often poor, rarely providing girls the opportunity for academic success. Systemic issues that increase the likelihood of inappropriate detention of girls are the tendency to incarcerate girls for minor offenses and technical violations of probation and parole. They are also detained as a direct and indirect result of family violence and due to the failure of systems to work together. 29 selected readings and a list of 13 resources