Conceptual understanding is widely regarded as an important aim in an introductory physics course at high school, college, or university level. However, this goal invites two important questions: firstly, what does conceptual understanding entail, and secondly, what kind of instructional approach might be efficient in imparting conceptual understanding to students? In this book the notion of students' conceptual coherence is introduced to clarify what is meant by conceptual understanding. Students' conceptual coherence is divided into three aspects: contextual, representational, and conceptual framework coherence. The abilities required by the conceptual coherence are discussed as well as ways of evaluating it in the case of the force concept. A new research-based instructional approach to foster students' conceptual coherence of the force concept and related kinematics is introduced and validated: it brings together interactive-engagement teaching methods and the research on students' difficulties with the target domain. This book is aimed at researchers in physics and science education and physics instructors.