Abstract. This article is devoted to the explanation of the onset of localization and the formation of shear bands in high strain-rate plasticity of metals. We employ the Arrhenius constitutive model and show Hadamard instability for the linearized problem. For the nonlinear model, using an asymptotic procedure motivated by the theory of relaxation and the Chapman-Enskog expansion, we derive an effective equation for the evolution of the strain rate, which is backward parabolic with a small stabilizing fourth order correction. We construct self-similar solutions that describe the self-organization into a localized solution starting from well prepared data.Key words. shear bands, localization, effective equations, self-similarity.1. Introduction. The phenomenon of shear strain localization appears in several instances of material instability in mechanics. It is associated with ill-posedness of an underlying initial value problem, what has coined the term Hadamard-instability for its description in the mechanics literature. It should however be noted that while Hadamard instability indicates the catastrophic growth of oscillations around a mean state, it does not by itself explain the formation of coherent structures typically observed in localization. The latter is a nonlinear effect that will be the center-stage of the present study.The mathematical theory of localization in high strain rate plasticity aims to understand a destabilizing feedback mechanism proposed in [20,3] and deemed responsible for formation of shear band. It poses analytical challenges at the interface of dynamical systems theory and (small viscosity) parabolic regularizations for ill-posed problems. The onset of localization may be decomposed into two stages. At the first stage (a) one aims to determine whether a Hadamard-type instability is at play for a linearized problem. The second stage (b) requires to understand how the Hadamard instability interacts with the nonlinear features of the problem to form a localized coherent state, associated to a shear band. The latter is a challenging problem in the realm of nonlinear analysis. In this survey we draw material from [10,11,1] and focus on the Arrhenius law as a paradigm to describe the sequence of events occurring in the process of localization.