The dynamic process underlying the irreversible (plastic) deformation of crystalline materials under constant stress involves the motion of a large number of interacting dislocations. Recent experiments and numerical models show that the deformation dynamics in pure systems at mesoscopic scales exhibits features such as intermittency and scaling. These findings enrich the classical picture of the process and emphasize the complex behavior of these topological defects which can be found in several materials, like high T_c superconductors, liquid crystals and most solids. We will first briefly introduce the basic features of dislocations and some constitutive laws for plastic deformation. Then, we will present and discuss the new evidence that has encouraged us to tackle this phenomenon within the non-equilibrium statistical mechanics scenario.