Rehabilitation of patients following anterior cruciate ligament (ACL) reconstruction has undergone remarkable improvements over the past two decades. During this time, ACL research has been at the forefront of many orthopaedic and sports physical therapy clinics. With over 20 years of ACL rehabilitation experience (senior author) and prior collaboration with accelerated ACL rehabilitation pioneer K. Donald Shelbourne, the authors wish to present a unique perspective on the evolution of ACL rehabilitation.Prior to the classic article by Paulos et al in 1981,(1) literature on ACL rehabilitation was quite sparse. The basis for ACL rehabilitation at this time was founded in basic science studies conducted with animal models. In an effort to protect the graft, emphasis was placed on immobilization, extension limitation, restricted weight bearing, and delayed return to activity. Despite achieving good ligamentous stability, patients often experienced a spectrum of complications.In 1990, Shelbourne and Nitz(2) proposed an accelerated rehabilitation protocol following ACL reconstruction based on clinical experience. Their program emphasized delayed surgery, earlier range of motion and weight bearing, and full extension. As a result, patients experienced better clinical outcomes while maintaining knee stability.The rehabilitation program presented in this paper is still largely based on the principles of the accelerated protocol. As evidence-based practice and the call for prospective, randomized clinical research continues, the continued progress in treating patients with this injury will be enhanced. Furthermore, clinicians are urged not to lose sight of the clinical reasoning that helped evolve the ACL rehabilitation process where it is today.