This chapter serves as an introduction to Disciplinary Core Ideas (DCIs). As a whole, DCIs help students build usable knowledge that is central to the physical sciences but also across the life sciences, Earth and space sciences, and engineering. These core ideas also form a strong foundation that allows individuals to continue learning throughout their lives. DCIs are critical within and across the various science disciplines. Building understanding of the DCIs is critical because it allows learners to solve real-world problems and further develop understanding in conjunction with the science and engineering practices and crosscutting concepts. Because of their power to explain phenomena, DCIs serve as important intellectual tools. 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.