Osteoarthritis (OA) is the most common form of arthritis and the prevalence of OA increases with age. it is the major contributor to functional impairment in older adults. Symptomatic knee OA prevalence is reported to be 13% among adults over 55 years old. OA process not only affects the articular cartilage, but involves the entire joint, including the subchondral bone, capsule, ligaments, synovial membrane, and periarticular muscles and represents the failure of an organ (the synovial joint). OA is initiated by a mechanical damage to the joint and it is a manifestation of attempts to heal the joint and ameliorate the abnormal biomechanics. The distinction between primary and secondary OA is not meaningful as OA is always secondary to another disease or condition. The diagnosis of OA in clinical practice should be made on the basis of history and physical examination. Radiography is needed to confirm clinical suspicion and rule out other conditions. Other inflammatory diseases, predisposing diseases to OA and local causes of knee pain are potential differential diagnoses. Treatment modalities for knee OA are non-pharmacological, pharmacological, intra-articular and surgical. The management of OA should be tailored for each patient and treatment guidelines should be taken into consideration. In this article the current treatment guidelines are reviewed in details. Turk J Phys Med Rehab 2009; 55 Suppl 1: 1-7.