The emergence in the deforming material of local strain patterns (self excited waves), which are ordered in space and evolve with time, has been investigated for a wide range of metals and alloys. The main parameters of these waves, i.e. propagation rate against work hardening coefficient, dispersion law and wavelength against specimen length and grain size, have been defined. The possibility of treating plastic flow localization as a process of plastic flow occurring in a deforming medium is considered. A set of equations has been developed, which is appropriate for the description of the evolution of local strain domains. The changes in the type of local strain pattern observed in the various stages of flow are examined. A model is proposed to account for the large-scale periodicities exhibited by the distribution of localized deformation.