Osteoarthritis is the most common joint disorder in the world and its incidence is rising. In Western populations it is one of the most frequent causes of pain, loss of function and disability in adults. The estimated lifetime risk for knee osteoarthritis is approximately 40% in men and 47% in women. The diagnosis of osteoarthritis is complex due to a lack of specific physical and/or laboratorial findings. The American College of Rheumatology (ACR) has recommended using the following criteria for the diagnosis of knee osteoarthritis: chronic knee pain (lasting for more than 6 weeks) and at least three of the following: • Age over 50 years old. • Morning knee stiffness lasting up to 30 minutes. • Crepitus with active motion • Tenderness on bony palpation • Thickening or growth of the bones • No local heat on palpation Treatment of osteoarthritis involves alleviating pain, attempting to rectify mechanical misalignment, and identifying and addressing manifestations of joint instability. The American Academy of Orthopedic Surgeons (AAOS) has conducted a systematic review of the current scientific and clinical research and has issued clinical practice guidelines containing fifteen recommendations for the treatment of osteoarthritis of the knee, and include only less invasive alternatives to total or partial knee arthroplasty. This review presents the background, diagnosis, treatment and a summary of the AAOS guidelines regarding "Treatment of Osteoarthritis of the Knee".