This book, based on a recent German publication, offers an overview of basic data and recent developments in the groundbreaking field of molecular allergology. It comprehensively explores the origin and structure of single allergen molecules ( components ) and their utility in improving the management of type I, IgE-mediated allergic reactions and disorders like allergic respiratory diseases, food allergies, and anaphylaxis. Highly specific testing, called component-resolved diagnostics, aims to identify and utilize single molecules. Over 200 single allergens from plant or animal sources have been applied to single or multiplex laboratory testing for the presence of allergen-specific IgE.