In this thesis we investigate different phases of matter in systems driven out of equilibrium. In particular, we focus on current driven metal insulator transitions and on the physics of negative conductivity in photoexcited metals. We present a new mechanism by which a modest applied electric field can destabilize a correlated insulating phase at finite temperature, without directly exciting carriers across the gap. We investigate the consequences of a metal insulator phase interface, and show that the large difference in Seebeck coefficients leads to a substantial heat generation or removal at the interface depending on the direction of the applied electric current; our findings explain the key features of recent interesting experiments in Calcium Ruthenate. We also analyze a model of a metal coupled to a strongly photoexcited phonon mode and show that under general conditions the system exhibits a negative conductivity, even long after the removal of the pump; we study the phenomenological consequences of such state and find that it leads to a novel and purely non-equilibrium collective mode coupling charge and entropy. The resonance of this mode with probe radiation induces an enhancement of the optical reflectivity and can explain the experimental reports of the non-equilibrium state in photoexcited fullerides.