  The chapter presents the problem of the complexity of plastic flow in alloys,
which is manifested by serrated deformation curves and transient plastic strain
localizations. This phenomenon uncovers an inherently collective nature of the
dynamics of crystal defects. The chapter discusses the state-of-the art of this
research under the angle of distinct regimes of collective dislocation dynamics
found in conventional, basically binary alloys, e.g., self-organized
criticality, deterministic chaos, or synchronization. It concludes with the
formulation of diverse open questions, notably concerning manifestations of the
collective dislocation dynamics pertaining to finer scales of plastic
deformation processes, as compared to the macroscopic plastic instability.
