This review deals with one aspect of the fundamental optical properties of metal nanoparticles: the dynamics that occur following absorption of photons. Rather than being a narrow topic, this is a tremendously diverse subject with many different types of experimental studies. Understanding the sequence of events following photon absorption and their time scales under- pins many of the applications of metal nanoparticles. For example, the successful use of metal nanoparticles in photother- mal therapy,21-28 where laser excitation is used to selectively kill cells, is because metals rapidly convert the absorbed photon energy into heat. The different photophysical processes are discussed in chronological order, that is, starting with optical absorption and dephasing of the LSPR, going through internal relaxation of the electrons via electron-electron scattering and electron-phonon coupling, and ending with energy dissipation in the environment.38-43 The review concentrates on noble metal nanoparticles, as these have been the most studied. There are several reasons for this: recipes are available for making noble metal particles with good control of size and shape,1-10 the particles are resistant to oxidation, and they have plasmon resonances in the visible to near-IR region of the spectrum,33-36 so they can be easily studied.