The development and the present state of a few key aspects of the theory of plasticity are sketched as a guide to the literature for those new to or not centrally involved in the subject. Only a small fraction of this extensive literature is cited. Special attention is paid to the frequently inspirational but more often misleading influence of the theory of elasticity and the role of initial isotropy. The required simplicity of stress-strain relations to be usable with the most powerful of computers, for the analysis or design of metalworking processes or of ductile engineering structures and devices, is contrasted with the enormous complexity needed to model real behavior in quite crude detail. An attempt is made to place in perspective a variety of older and current representations, both conventional and unconventional. Applicable regimes of transference of results between the atomic, dislocation, or single crystal level and the macroscopic or continuum level also are explored.