The athlete’s knee is exposed to various degrees of sporting activity, injury, and chronologic aging effects, which frequently result in a spectrum of meniscal, ligamentous, and articular cartilage disorders. Participation in routine and competitive sports may result in a higher incidence of acute and chronic injury, chronic overuse syndromes, and osteoarthritis. One of the goals of this chapter is to introduce a new concept, chondropenia, the earliest degenerative cartilage lesion, and highlight and highlight its pathogenesis leading to the end-stage articular cartilage lesion, osteoarthritis. The “chondropenia curve,” a working concept, is also introduced. A treatment algorithm for knee articular cartilage injuries, based on the current understanding of the natural history of cartilage injuries and the current state-of-the-art treatments, is covered in detail. The emphasis of this algorithm is on preservation of long-term joint function.