Bone marrow lesions of the knee in patients with osteoarthritis (OA-BML) are an important clinical entity that may explain progressive pain, decreased quality of life, and impaired function. MRI of OA-BMLs demonstrates a region of subchondral bone with hyperintense marrow signal on T2-weighted images. Histopathology retrieval studies have demonstrated that these lesions correlate with microdamage of the trabecular bone, and subsequently, this leads to a vicious cycle of subchondral bone attrition, attempts at repair, pain, and progressive deformity. These lesions have also been linked to accelerated loss of adjacent articular cartilage and increases in the severity of knee pain, prompting patients to seek musculoskeletal care and treatment. Multiple studies have also correlated the presence of an OA-BML with an increased probability of seeking knee arthroplasty. Knowledge of these lesions is important in the context that knee OA is both a cartilage-based and bone-based disease. Further study of OA-BMLs may provide opportunities for early intervention and OA disease–modifying treatments.