Activity-Based Physics is a multi-institutional project to sustain and enhance current efforts to render introductory physics courses more effective and exciting at both the secondary and college level. This program represents a collaborative effort by an informally constituted team of educational reformers to use the outcomes of physics education research along with flexible computer tools to develop activity-based models of physics instruction. This project includes the refinement of existing written materials, apparatus, instructional techniques, and computer software and hardware; the creation of new instructional materials and approaches; as well as classroom testing in different settings and dissemination. The refinement and development of instructional strategies and materials is informed by a comprehensive program of educational research.