This chapter follows proper anatomic practice and refers all spatial relationships and movements to the “anatomic position”: erect stance, feet together, head level with eyes to the front, upper limbs by the sides with forearms supinated, and digits extended. Secondary cartilaginous joints—symphyses—all occur in the midsagittal plane and allow varying degrees of movement while withstanding compressive forces. The chapter discusses aspects of the functional anatomy of synovial joints. Traditionally, factors maintaining joint stability are regarded as the shape of the articular surfaces, ligaments, and muscles. Other ligaments may be attached close to axes of motion and provide some or all of the stability in certain planes. These ligaments give lateral stability to the joint throughout its range of flexion-extension, protecting it from adduction-abduction and lateral shear forces. Similarly, the conjunct movements of the first carpometacarpal joint follow the habitual arc of movement of the thumb as it takes up varying degrees of opposition to the fingers in fine manipulation.