The hypersensitivity of the immune system in response to harmless substances in the environment is referred to as an allergy. Allergies are common in society, with a significant percentage of the population affected by atopic dermatitis, allergic rhinitis, food allergies, asthma, anaphylaxis, etc. A wide range of foods cause allergic reactions, such as eggs, soy, cow’s milk, peanuts, etc. Insect stings can also generate allergic responses. An allergic response to a trigger starts when the immunoglobulin E antibodies bind to the allergen and then to a receptor on mast cells where it triggers the release of histamine and other inflammatory chemicals. The management of allergies is under the scope of clinical immunology. The professionals specialized in this field are known as clinical immunologists. This book traces the progress of clinical immunology and highlights some of its concepts and principles. Also included in this book is a detailed explanation of the mechanisms and manifestations of diverse kinds of allergies. A number of latest researches have been included to keep the readers up-to-date with the global concepts in these areas of study.