Though nonequilibrium phenomena abound in nature, they are still only very poorly understood at a fundamental level. Even the study of nonequilibrium steady states, as the simplest generalizations of thermal equilibrium, is still in its early stages. However, investigations of simple model systems have revealed a wealth of unexpected behavior which can appear highly counterintuitive when compared to our equilibrium-trained expectations.
In my talk, I will review the unusual properties displayed by a particular model class, namely, driven diffusive systems. These are simple lattice gases, characterized by conserved particle densities and dynamical rules which break detailed balance. Their physical applications include fast ionic conductors, traffic problems, microemulsions and electrophoresis. These simple models show unexpected phase transitions, novel universality classes, and anomalous correlations even in disordered phases. A number of open questions will be discussed.