Abstract : The shear strength properties of granular materials reﬂect their inherent force and fabric anisotropy. We analyze the role of fabric and force anisotropies with respect to the critical-state shear strength. Then, a model of accessible geometrical states in terms of particle connectivity and contact anisotropy is presented. This model incorporates in a simple way the fact that, due to steric exclusions, the highest levels of connectivity and anisotropy cannot be reached simultaneously, a property that affects seriously the shear strength. We also analyze the force anisotropy in the light of the speciﬁc role of weak forces in sustaining strong force chains and thus the main mechanism that underlies anisotropic force patterns. Finally, we brieﬂy discuss the effect of interparticle friction, particle shape, and adhesion.