The knee joint is amongst the most commonly injured joints in the human body, and ultrasound has played an increasingly important role in accurate diagnoses of various structural pathologies. Given the generally superficial location of the knee, a high frequency linear probe is frequently used to identify various knee abnormalities, such as medial or lateral collateral ligament tear, tendinopathy, and bursitis. The more internal structures, such as the menisci and cruciate ligaments, can be a bit more difficult to visualize, nonetheless partial imaging of these structures still proves valuable. This chapter will review the sonoanatomy, structural pathology and when applicable, injection techniques for the knee joint under ultrasound guidance.