Written and edited by experts in the field, this collection from Cold Spring Harbor Perspectives in Medicine covers the progress that has recently been made in our understanding of the pathophysiology of prion diseases, as well as ongoing efforts to develop effective therapeutics. The contributors discuss how proteins such as tau, islet amyloid polypeptide, and alpha-synuclein adopt alternative shapes that lead them to aggregate, resulting in cellular degeneration. Therapies for human and animal diseases caused by prions are also covered. This volume is therefore useful for all biomedical scientists and physicians wishing to understand and treat this expanding group of devastating disorders.