This introductory level text addresses the broad range of nonequilibrium phenomena observed at short time scales. It focuses on the important questions of correlations and memory effects in dense interacting systems. Experiments on very short time scales are characterized, in particular,  by strong correlations far from equilibrium, by nonlinear dynamics, and by the related phenomena of turbulence and chaos. The impressive successes of experiments using pulsed lasers to study the properties of matter and of the new methods of analysis of the early phases of heavy ion reactions have necessitated a review of the available many-body theoretical methods. The aim of this book is thus to provide an introduction to the experimental and theoretical methods that help us to understand the behaviour of such systems when disturbed on very short time scales. The contributions are written in a tutorial style and are largely self-contained, allowing graduate students and researchers alike to become familiar with this exciting interdisciplinary field.