This article presents current information concerning (a) the structural relationships of the Golgi tendon organ (GTO) with different types of extrafusal muscle fibers; (b) the Gp.Ib reafferent or feedback fibers from the GTO; (c) the way in which these proprioceptors monitor muscle tension and function in parallel processing with other receptors and with the central control mechanisms of the nervous system; and (d) how GTO’s are involved in regulating autogenic excitation, autogenic inhibition, or co-contraction of extrafusal muscle fibers.