Knee pain is one of the most common musculoskeletal complaints in primary care medicine. The leading causes of knee pain are osteoarthritis and musculoskeletal disorders. A careful history and a rigorous clinical examination usually enable a diagnosis to be made without the need for further investigations. A systematic search for red flags helps identify patients requiring urgent and specialized care. When necessary, X-rays and ultrasound are the first-line imaging tests to perform. The latter can be used to guide a joint puncture for diagnostic and therapeutic purposes. This article reviews the diagnostic approach and summarizes the management of the main pathologies encountered in the general practitioner's office.