Osteoarthritis of the knee is one of the most common degenerative disorders of the musculoskeletal system and a leading cause of chronic pain and functional disability, especially among older adults. With the global increase in life expectancy, rising obesity rates, and reduced physical activity, this condition has become a growing health burden, highlighting the importance of conservative interventions—particularly physical therapy—in slowing its progression and improving patients’ quality of life. This condition develops as a result of the gradual degeneration of the articular cartilage that covers the ends of bones within the knee joint. The cartilage loses its elasticity and its ability to absorb shock, leading to increased friction between joint surfaces. The changes are not limited to the cartilage alone but also involve the subchondral bone, synovial membrane, ligaments, and surrounding muscles, making the condition multifactorial and more complex than previously thought as a simple mechanical wear-and-tear process. Several factors contribute to the development of knee osteoarthritis, including aging, chronic mechanical stress, previous injuries such as ligament or meniscal tears, and obesity, which significantly increases joint load. Genetic factors and poor lower limb alignment (such as varus or valgus deformities) also play a role in accelerating degenerative changes. Studies have shown that weakness of the quadriceps muscle is a major factor in worsening symptoms and disease progression. Patients typically experience gradual knee pain that worsens with physical activities such as walking or climbing stairs and improves with rest. Stiffness is also common, particularly after periods of inactivity, though it is usually short-lived. Other symptoms may include a grinding sensation or clicking sounds during movement, reduced range of motion, and decreased joint stability. In advanced stages, visible deformities may develop, making daily activities increasingly difficult. Diagnosis relies on a combination of patient history and clinical examination, including assessment of pain, range of motion, muscle strength, and alignment. X-rays are the most commonly used imaging tool, revealing joint space narrowing, osteophyte formation, and increased subchondral bone density. MRI may be used when necessary to evaluate soft tissues and detect early changes. Physical therapy is considered the cornerstone of non-surgical management of knee osteoarthritis. Its goals are to reduce pain, improve function, and slow disease progression. Treatment typically begins with pain management using physical modalities such as heat or cold therapy, transcutaneous electrical nerve stimulation (TENS), and ultrasound therapy. However, the core of treatment lies in therapeutic exercise, which is the most effective long-term intervention. These exercises include strengthening the quadriceps and hamstring muscles, improving range of motion, and enhancing balance and neuromuscular control. Weight loss also plays a crucial role in reducing mechanical stress on the joint, as even a modest reduction in body weight can lead to significant symptom improvement. Manual therapy techniques, including joint mobilization and soft tissue manipulation, can further help reduce pain and improve mobility. In some cases, assistive devices such as braces or canes may be used to decrease joint load. Recent research indicates that knee osteoarthritis involves low-grade inflammation, which helps explain the persistence of symptoms even without significant mechanical stress. Therefore, modern treatment approaches emphasize comprehensive rehabilitation programs that integrate exercise, patient education, and lifestyle modification, rather than relying solely on pharmacological treatments. In conclusion, knee osteoarthritis is a complex chronic condition that requires a comprehensive and multidimensional approach. Physical therapy has proven to be an essential and effective option in managing this condition by improving muscle strength, restoring functional mobility, and reducing pain. Early diagnosis, adherence to rehabilitation programs, and adopting a healthy lifestyle are all critical factors in achieving better outcomes and slowing disease progression over time. Al-Mustaqbal University, the first university in Iraq