When a molecule is core-excited to a dissociative state, dissociation may occur on the time scale of the core hole decay, i.e. a few femtoseconds. This is discussed in terms of the nuclear dynamics of the dissociation, and the electronic dynamics of the core hole decay. Examples demonstrating different aspects of these phenomena are presented. Semi-classical methods, which provide quantitative information about the dissociation
dynamics, are outlined. More advanced theories, including time-dependent quantum mechanics and interference, as well as possible experimental developments, are briefly discussed.