Chronic pain in the knee joint is most commonly caused by osteoarthritis, especially in elderly patients but can be due to other causes, such as rheumatoid arthritis. The diagnostics include an exact patient medical history and a clinical examination, which often already provide clear indications of the cause of the knee pain. Subsequently, further diagnostics can then be considered, such as radiological procedures and laboratory diagnostics. The treatment is determined by the cause and the individual patient and aims to reduce pain and to preserve the mobility of the joint. Generally, therapy consists of pain management and physiotherapy as well as alternative therapeutic procedures, mostly in combination. Proximal tibial opening wedge osteotomy can be useful; however, partial or total knee arthroplasty should only be considered when conservative treatment options have been exhausted.