The authors analyze the functions of the synovial membrane and the chemical-physical properties of synovial fluid. In particular they evaluate the role played by synovial fluid in the complex mechanism of the temporomandibular joint. Every single part that belongs to the temporomandibular joint, together with the stomatognathic apparatus, plays a specific and particular role according to the dynamics and to the preservation of the correct temporomandibular joint physiology. The physiological postural and functional relationship between the various parts of the temporomandibular joint is guaranteed by a number of biomechanical restrictions that lead and influence the regular execution of the articular movements. The most involved biomechanical restrictions in the temporomandibular joint are the temporomandibular ligament, the lateral disc ligament, the bilaminar zone or retrodiscal tissue, the synovial membrane, and the synovial fluid.