Allergy is one of the major health problems of most modern societies. Although allergic diseases are well-known for almost two hundred years, their prevalence has increased dramatically over the last decades. Allergic reactions manifest in various organs, most commonly in the skin and mucous membranes, the frontier surfaces where the contact between the individual and the environment takes place. In a very concise and practical way this book covers all aspects of allergic reactions from pathophysiology to diagnosis, therapy and prevention with a strong focus on relevant aspects for the everyday work of the practising dermatologist and allergist in the hospital or office. This book reflects the rich personal experience of a German allergist with international training and reputation, who is active in immunology and allergy research and practice for almost 30 years. In this book, not only IgE-mediated allergic reactions are covered but all other kinds of allergies such as atopic eczema, contact dermatitis, drug eruptions, anaphylaxis and food allergies are equally represented as well as psychosomatic aspects and problems of environmental intolerances.