Abstract: Randomized controlled trials continue to be at the pinnacle of the evidence hierarchy. With this unique vantage point, they inform medical practice, clinical guidelines, health policy, and reimbursement. Prior to an emphasis on randomized controlled trials, traditional clinical research consisted primarily of uncontrolled case series and expert opinions. Randomized controlled trials are a true experiment in clinical practice and provide the most valid answers to clinical questions by reducing bias originating from patients, providers, and investigators. Riding on the coattails of other medical subspecialties, orthopaedic surgeons have recognized the importance of evidence-based medicine. From 1975 to 2005, the number of Level-I studies increased over fivefold and comprised >20% of studies published in The Journal of Bone and Joint Surgery (American Volume) (JBJS). With the emergence of comparative effectiveness research, the definition and methods of best evidence may continue to evolve. In conclusion, substantial improvements in both the quantity and the quality of randomized controlled trials in orthopaedic surgery have occurred, although unique considerations still limit their widespread use.