Advances in optical technology, instrumentation and implants now enable arthroscopic surgery to be performed on all large joints and most small joints of the limbs. Arthroscopic techniques are usually a development of surgical procedures previously performed through a large open incision, although the critical element of each procedure (for example removal of a torn meniscus) usually remains unchanged. The smaller size of incisions and reduction in tissue damage associated with arthroscopic surgery can reduce morbidity and complications. Therapeutic arthroscopy now encompasses excision, reconstruction and replacement of damaged or abnormal tissue. Improvements in the accuracy of MRI, CT and high-definition ultrasonography have limited the use of diagnostic arthroscopy to rare indications, but in the past 10 years the rates of some arthroscopic surgeries have increased by over 7-fold. Considerable variation in the type and utilization of arthroscopic procedures exists in practice, partly explained by the slow diffusion of new techniques and technology, but also by differences in clinician and patient beliefs and expectations. This Review reflects on both the success of arthroscopy and the general lack of evidence-based assessment of the efficacy and cost-effectiveness of arthroscopic procedures-a clear sign that more clinical trials in this field are required.