Osteoarthritis (OA) is a widely prevalent disease worldwide and, with an increasing ageing society, is a challenge for the field of physical and rehabilitation medicine. Technologic advances and implementation of sophisticated post-processing instruments and analytic strategies have resulted in imaging playing a more and more important role in understanding the disease process of OA. Radiography is still the most commonly used imaging modality for establishing an imaging-based diagnosis of OA. The need for an effective non-surgical OA treatment is highly desired, but despite on-going research efforts no disease-modifying OA drugs have been discovered or approved to date. MR imaging-based studies have revealed some of the limitations of radiography. The ability of MR to image all relevant joint tissues within the knee and to visualize cartilage morphology and composition has resulted in MRI playing a key role in understanding the natural history of the disease and in the search for new therapies. Our review will focus on the roles and limitations of radiography and MRI with particular attention to knee OA. The use of other modalities (e.g. ultrasound, nuclear medicine, computed tomography (CT), and CT/MR arthrography) in clinical practice and OA research will also be briefly described. Ultrasound may be useful to evaluate synovial pathology in osteoarthritis, particularly in the hand.