Positive behavior support (PBS) has been a dynamic and growing enterprise for more than 25 years. During this period, PBS has expanded applications across a wide range of populations and multiple levels of implementation. As a result, there have been understandable inconsistencies and confusion regarding the definition of PBS. In this essay, we offer an updated and unified definition. We provide a brief historical perspective and describe a process for developing a proposed definition. We also discuss the rationale for key elements of the definition.