New Moves is a school-based physical education (PE) intervention aimed at preventing weight-related problems in adolescent girls by increasing their physical activity, improving their body image and self-worth, and improving their diet. The primary component of New Moves is an all-girls PE class that is designed to provide participants with a noncompetitive, supportive environment in which they are encouraged to be physically active regardless of size, shape, or skill level. The intervention’s theoretical model of change is based on social cognitive theory and addresses a combination of socioenvironmental, personal, and behavioral factors.