This article uses a historical framework to review the rehabilitation treatment taxonomy (RTT). The needs and challenges in creating a comprehensive classification system for rehabilitation treatments are identified based on review of (1) the development of other biological classification systems and (2) the historical foundations for rehabilitation and related theoretical underpinnings. The historical overview is used to identify needs for refining the RTT, including (1) changes needed in the structure of the RTT to address the varied roles of environmental factors in the rehabilitation treatment process, (2) changes needed to link the RTT with clinical documentation and third-party reimbursement, and (3) revisions in the nomenclature for the RTT to enhance clear communication. Finally, challenges with the next steps in developing a comprehensive classification system for rehabilitation are discussed, including (1) the complexity needed to classify a dynamic process and to account for the agents, mechanisms, and objects targeted by that process and (2) the importance of a continued multidisciplinary approach to ensure a classification system that will be broadly useful for a highly diverse and rapidly evolving field. © 2014 by the American Congress of Rehabilitation Medicine.