This book provides an introduction to localised excitations in spatially discrete systems, from the experimental, numerical and mathematical points of view. Also known as discrete breathers, nonlinear lattice excitations and intrinsic localised modes, these are spatially localised time periodic motions in networks of dynamical units. Examples of such networks are molecular crystals, biomolecules, and arrays of Josephson superconducting junctions. The book also addresses the formation of discrete breathers and their potential role in energy transfer in such systems.Contents:Computational Studies of Discrete BreathersVibrational Spectroscopy and Quantum LocalizationSlow ManifoldsLocalized Excitations in Josephson ArraysProtein Functional Dynamics: Computational ApproachesNonlinear Vibrational Spectroscopy: A Method to Study Vibrational Self-TrappingBreathers in Biomolecules?Statistical Physics of Localized VibrationsLocalization and Targeted Transfer of Atomic-Scale Nonlinear Excitations: Perspectives for ApplicationsReadership: Advanced graduate students and postdoctoral researchers in nonlinear dynamics.