Modeling of the evolution of distributed damage and plasticity such as micro-cracking, void formation, dislocation densities, and shear bands necessitates strain-softening constitutive models. The nonlocal continuum concept has emerged as an effective means for regularizing the (initial) boundary value problems with strain softening, capturing the size effects observed in experiments, capturing small-scale deviations from local continuum models caused by material heterogeneity, and avoiding spurious localization that gives rise to pathological mesh sensitivity in numerical computations. This book discusses the integral and gradient formulations of nonlocality, computational aspects, and comparison of approaches and emphasizes recent developments in the bridging of material length scales.