The evolution of systems driven outside of thermodynamic equilibrium is characterized by strong nonlinearity and the formation of complex spatio-temporal patterns. We illustrate several key concepts by focusing on three prototypical situations: Rayleigh-Benard convection, Faraday waves, and defect motion in soft matter. In the first case, we discuss the appearance of non variational effects in an otherwise overdamped dynamical system, and how they lead to spiral defect chaos, an extended spatio temporally chaotic state. In the second, weak dissipation effects in a near Hamiltonian system account for the formation of quasi crystalline patterns on the surface of a vibrated fluid layer. In the latter case, we discuss topological defect motion in modulated phases, and mechanisms underlying the emergence of long range order.