Metallothioneins (MTs) represent a large family of proteins characterized by high heavy metal content (mainly CuII and ZnII) and by an unusual cysteine abundance. They have a powerful protective function in all animal tissues, due most likely to their properties as free radical scavengers protecting against oxidative damage. Moreover, the presence and overexpression of MTs in various pathological conditions, such as metal dyshomeostasis, cell proliferation, neurological disorders, and chemotherapy and radiotherapy resistance, could be used as an important prognostic marker, as a histopathological diagnostic tool, and to follow specific pharmacological treatments.This important book explores the role of MTs in the field of neurological disorders (brain inflammation, Alzheimer's and prion diseases, autism, ALS, etc.), cardiology (cardiomyopathy, atherosclerosis), and oncology (melanoma, prostate and breast cancer), through authoritative contributions and a description of basic biochemical information and paradigmatic pathological events.