Tinnitus is the perception of a sound when no external sound is present. The severity of tinnitus varies but it can be debilitating for many patients. With more than 100 million people with chronic tinnitus worldwide, tinnitus is a disorder of high prevalence. The increased knowledge in the neuroscience of tinnitus has led to the emergence of promising treatment approaches, but no uniformly effective treatment for tinnitus has been identified. The large patient heterogeneity is considered to be the major obstacle for the development of effective treatment strategies against tinnitus. This eBook provides an inter- and multi-disciplinary collection of tinnitus research with the aim to better understand tinnitus heterogeneity and improve therapeutic outcomes.