This volume presents a comprehensive introduction to the study of nuclear structure at finite temperature. By measuring the frequencies of the high-energy photons emitted or absorbed by an atomic nucleus it is possible to visualize the structure of that nucleus. In such experiments it is observed that the atomic nucleus displays resonant behavior, absorbing or emitting photons within a relatively narrow range of frequencies. To study emission processes one measures the y-decay of compound nuclei, and by this means it is possible to probe the structure of the nucleus at finite temperature. This book is divided into two main parts: the study of giant resonances based on the atomic nucleus ground state (zero temperature), and the study of the y-decay of giant resonances from compound (finite temperature) nuclei. As this work is an outgrowth of their lectures to fourth-year students at the University of Milan, the authors have placed special emphasis on the general concepts that form the foundation of the phenomenon of giant resonances. This basic subject matter is supplemented with material taken from work going on at the forefront of research on the structure of hot nuclei. Thus, this volume will serve as an essential reference for both young researchers and experienced practitioners.