An overview is given on the recent understanding of time asymmetry in nonequilibrium statistical mechanics. This time asymmetry finds its origin in the spontaneous breaking of the time-reversal symmetry at the statistical level of description. The relaxation toward the equilibrium state can be described in terms of eigenmodes of fundamental Liouville's equation of statistical mechanics. These eigenmodes are associated with Pollicott-Ruelle resonances and correspond to exponential damping. These eigenmodes can be explicitly constructed in dynamical systems sustaining deterministic diffusion, which shows their singular character. The entropy production expected from nonequilibrium thermodynamics can be derived ab initio thanks to this construction. In the escape-rate theory, the transport coefficients can be related to the leading Pollicott-Ruelle resonance of open systems and to the characteristic quantities of the microscopic dynamics. In nonequilibrium steady states, the entropy production is shown to result from a time asymmetry in the dynamical randomness of the nonequilibrium fluctuations. Furthermore, the generalizations of Onsager reciprocity relations to nonlinear response can be deduced from the fluctuation theorem for the currents. Furthermore, the principle of temporal ordering in nonequilibrium steady states is formulated and its perspectives for the generation of biological information are discussed.