The purpose of this talk is to present new homogenization schemes for the prediction of the mechanical behavior of elastic-viscoplastic heterogeneous materials. In a first part, Mori-Tanaka and self-consistent approaches are developed based on an interaction law postulated by Molinari et al (Mech. Mater., 26, 43, 1997). Illustrations are given for two phase composite materials. In a second part of the present talk, we would like to emphasize how a simple homogenization technique can be useful for the prediction of the mechanical behavior of nanomaterials. Based on previous rigid viscoplastic models proposed by Kim et al. (Acta Mater, 48:493, 2000) and Kim and Estrin (Acta Mater, 53:765, 2005), the nanocrystalline material is described as a two phase composite material. Using the Taylor-Lin homogenisation scheme in order to account for elasticity, the yield stress of nanocrystalline materials can be evaluated. The transition from a Hall-Petch relation to an inverse Hall-Petch relation is defined and is related to a change in plastic deformation mode in the crystallite phase from a dislocation glide driven mechanism to a diffusion-controlled process.