This chapter discusses the disciplinary core idea of forces and interactions which consists of three component ideas that are described here. If any idea is a core concept, it is the idea of forces and interactions. Forces affect every single thing in the world, every single second and every phenomenon involves forces at some level. It is important for all students to construct a deep understanding of forces, motion, and stability because they are involved in every phenomenon and every technology. A list of materials, teacher background information, assessment, standards, safety, and references are provided. This book selection also includes the Table of Contents, Foreword, Acknowledgments, About the Editors, Contributors, Appendix, Image credits, and Index.