Highly demanding engineering applications demand advanced materials in terms of strength, toughness and durability. In order to characterise the performance of these materials, advanced monitoring methods are also sought for, which supply the necessary information about the structural integrity in a non-destructive way. One of the techniques applied for real time monitoring of the damage process is Acoustic Emission (AE). AE is based on the elastic waves which propagate mainly after crack propagation incidents. This book examines the Acoustic Emission technique, as well as the need for advanced materials.