The Climate Schools: Alcohol and Cannabis Module is a universal harm-minimization school-based prevention program for adolescents aged 13-15 years. The core content of the program is delivered over the Internet using cartoon storylines to engage students, and teacher-driven activities reinforce the core information. The program is embedded within the school health curriculum and is easy to implement with minimal teacher training required. The program was developed in 2007 through extensive collaboration with teachers, students, and health professionals (N = 24) in Sydney, Australia and has since been evaluated (N = 764). This article describes the formative research and process of planning that formed the development of the program and the evidence base underpinning the approach. The study's limitations are noted.