The Kellgren-Lawrence (KL) classification is a widely used radiographic tool for diagnosing osteoarthritis (OA), particularly in the knee. Developed by Kellgren and Lawrence in 1957, the classification system assigns grades from 0 to 4 based on the severity of OA, with Grade 0 indicating no OA and Grade 4 signifying severe OA. The system was initially applied to eight joints, but its primary focus is on the knee, where it has shown high interobserver reliability (0.83). However, the KL classification has been criticized for its linear progression model, which may not accurately reflect the complex nature of OA progression. Recent studies have suggested that the Rosenberg view, a 45° posteroanterior flexion weight-bearing radiograph, may provide better interrater reliability and correlation with arthroscopic evidence of OA. Despite its limitations, the KL classification remains a valuable tool in clinical practice and research, often used in conjunction with other diagnostic methods to provide a comprehensive assessment of OA. Further research should focus on developing treatment algorithms based on classification grades to guide clinical decision-making.The Kellgren-Lawrence (KL) classification is a widely used radiographic tool for diagnosing osteoarthritis (OA), particularly in the knee. Developed by Kellgren and Lawrence in 1957, the classification system assigns grades from 0 to 4 based on the severity of OA, with Grade 0 indicating no OA and Grade 4 signifying severe OA. The system was initially applied to eight joints, but its primary focus is on the knee, where it has shown high interobserver reliability (0.83). However, the KL classification has been criticized for its linear progression model, which may not accurately reflect the complex nature of OA progression. Recent studies have suggested that the Rosenberg view, a 45° posteroanterior flexion weight-bearing radiograph, may provide better interrater reliability and correlation with arthroscopic evidence of OA. Despite its limitations, the KL classification remains a valuable tool in clinical practice and research, often used in conjunction with other diagnostic methods to provide a comprehensive assessment of OA. Further research should focus on developing treatment algorithms based on classification grades to guide clinical decision-making.