This book is the first monograph dedicated to the use of the total absorption technique in beta decay studies. It provides a detailed introduction to the beta decay process and all necessary know-how for the use of the total absorption technique. Total absorption spectroscopy (TAS) is the one of the very few techniques available that can provide nuclear decay data free from the Pandemonium effect (the systematic error causes the assignment of larger beta-decay probabilities than the real values to the lower lying levels). This book covers all aspects related to the use of this technique, from the preparation of an experiment to the algorithms required in the analysis of the data acquired. It also covers the most relevant applications of the technique, from nuclear structure (comparison with nuclear models, determination of nuclear shapes) to nuclear astrophysics and other more applied purposes such as the prediction of reactor decay heat and the primary antineutrino spectrum from nuclear reactors.