Articular cartilage is a specialized connective tissue in diarthrodial joints, providing a smooth, lubricated surface for articulation and load transmission with low friction. It lacks blood vessels, nerves, and lymphatics, and has limited intrinsic healing capacity. Its structure consists of a dense extracellular matrix (ECM) with chondrocytes, primarily composed of water, collagen, and proteoglycans. The ECM is divided into zones (superficial, middle, deep, and calcified) and regions (pericellular, territorial, interterritorial), each with distinct functions. The superficial zone protects deeper layers, the middle zone bridges superficial and deep zones, the deep zone resists compressive forces, and the calcified zone anchors cartilage to bone. Collagen, mainly type II, forms fibrils intertwined with proteoglycan aggregates, providing structural support. Proteoglycans, such as aggrecan, contribute to the ECM's osmotic properties, enabling it to resist compressive loads. Chondrocytes, the resident cells, maintain and repair the ECM but have limited replication capacity. The ECM's unique viscoelastic properties allow it to withstand high cyclic loads. Articular cartilage functions as a biphasic medium, with fluid and solid phases, and its biomechanical behavior is influenced by fluid pressure and collagen-proteoglycan interactions. Age affects cartilage composition and chondrocyte function, leading to zonal changes and reduced proteoglycan aggregates. MRI is a valuable tool for evaluating cartilage, with techniques like delayed gadolinium-enhanced MRI and sodium MRI providing insights into glycosaminoglycan content and proteoglycan distribution. Articular cartilage's mechanical behavior is crucial for joint health, and its preservation is essential for maintaining joint function. Damage or degeneration can lead to conditions like osteoarthritis, highlighting the importance of understanding its structure, composition, and function for treatment and repair strategies.Articular cartilage is a specialized connective tissue in diarthrodial joints, providing a smooth, lubricated surface for articulation and load transmission with low friction. It lacks blood vessels, nerves, and lymphatics, and has limited intrinsic healing capacity. Its structure consists of a dense extracellular matrix (ECM) with chondrocytes, primarily composed of water, collagen, and proteoglycans. The ECM is divided into zones (superficial, middle, deep, and calcified) and regions (pericellular, territorial, interterritorial), each with distinct functions. The superficial zone protects deeper layers, the middle zone bridges superficial and deep zones, the deep zone resists compressive forces, and the calcified zone anchors cartilage to bone. Collagen, mainly type II, forms fibrils intertwined with proteoglycan aggregates, providing structural support. Proteoglycans, such as aggrecan, contribute to the ECM's osmotic properties, enabling it to resist compressive loads. Chondrocytes, the resident cells, maintain and repair the ECM but have limited replication capacity. The ECM's unique viscoelastic properties allow it to withstand high cyclic loads. Articular cartilage functions as a biphasic medium, with fluid and solid phases, and its biomechanical behavior is influenced by fluid pressure and collagen-proteoglycan interactions. Age affects cartilage composition and chondrocyte function, leading to zonal changes and reduced proteoglycan aggregates. MRI is a valuable tool for evaluating cartilage, with techniques like delayed gadolinium-enhanced MRI and sodium MRI providing insights into glycosaminoglycan content and proteoglycan distribution. Articular cartilage's mechanical behavior is crucial for joint health, and its preservation is essential for maintaining joint function. Damage or degeneration can lead to conditions like osteoarthritis, highlighting the importance of understanding its structure, composition, and function for treatment and repair strategies.