The atomic nucleus, despite of being one of the smallest objects found in nature, appears to be large enough to experience phase transitions. In general, nuclear matter is believed to have liquid and gaseous phases as well as interesting combinations of them. This book reviews what is known theoretically and experimentally about these phases of nuclear matter and the mechanisms inducing transformations between them. Current theoretical models describing nuclear reactions at intermediate energies are presented, and, in particular, phenomenological techniques of analysis used in heavy-ion reaction are described for the benefit of the practitioners in the field.