This article focuses on the Incredible Years Teacher Classroom Management (IY TCM) intervention as an example of an evidence-based program that embeds fidelity and adaptation within its design. First, the core features of the IY TCM program along with the methods, processes, and principles that make the intervention effective are described. The importance of fidelity and methods for effectively measuring fidelity are discussed. In addition, support mechanisms (training, mentoring, consultation, and coaching) necessary to facilitate high fidelity of implementation of IY TCM are highlighted. The goal is to clarify the underlying principles and supports needed to effectively allow IY group leaders to disseminate the IY TCM among teachers with diverse backgrounds and skills, who work with students with varying developmental, academic, and social-emotional needs. Often fidelity and adaptation are thought of as mutually exclusive, but in the IY model they are considered both complementary and necessary. Implications for school psychologists and prevention science are discussed. (Contains 1 table and 3 figures.)