The knee joint is affected in up to 30% of all sport injuries. A minor precentage of it are tendon injuries. For acute tendon injuries, quadriceps tendon rupture and patellar tendon rupture are most frequent. Beside that, ruptures of distal hamstring tendons or the popliteus tendon may occur. For chronic tendon injuries in sports, the jumpers knee and the runners knee are most frequent. Also insertional enthesopathy of the quadriceps tendon, of the iliotibial band, of the hamstring tendons may occur, furthermore a tendinitis or bursitis at the pes anserinus. These injuries are explained in this article focussing on symptoms, diagnostics and therapy.