This paper focuses upon the theoretical foundations of the modeling of elastoplastic polycrystalline aggregates. As a starting point, the known constitutive framework for a time-independent elastic-plastic material with a finite number of internal mechanisms of plastic deformation obeying the normality flow rule is adopted at a mesoscopic level (Subsection 10.2.1). Implications of that assumption for the macroscopic properties of a heterogeneous material have been studied theoretically and numerically in a number of papers. No survey of previous results is attempted here, rather, the aim of this article is to present nowel qualitative conclusions. In Subsection 10.2.2 the transmissibility of the structure of incremental constitutive relationships from the meso- to macro-level is proved for a spatially discretized aggregate, and expressions are derived for macroscopic effective hardening moduli. This goes beyond earlier results concerning the transition rules expressed in terms of the strain or stress rates and of the fourth-order tensors of instantaneous moduli or compliances.