The use of a mobile-bearing knee system is routine in modern total knee arthroplasty (TKA). There are indications for use of a mobile-bearing TKA for a growing number of patients. The design, however, was not always well appreciated. Fears of perioperative difficulties and lack of understanding of the design principles limited the acceptance of mobile-bearing technology. Recent evidence has shown that use of mobile-bearing prostheses in TKA has increased, and today, nearly three decades after its introduction, the mobile-bearing design remains relavent and important. The theories behind the design of mobile-bearing prostheses have shown in clinical practice what many already believed to be true: mobile-bearing TKA, when performed correctly, is reliable, and capable of providing substantial benefit for patients.