The book "The Fundamentals of Hypersensitivity and Allergy" comprises of seven chapters and describes the historical perspective, causes and classification of hypersensitivities, which are important in understanding the current issues regarding conditions in which the immune system which normally serves a protective role has a harmful effect. This book describes the original concept of hypersensitivity and allergy and how sensitive individuals respond to different allergens, drugs and other agents, where the body reacts with an exaggerated immune response that ultimately results in tissue damage. The classification of hypersensitive reactions given by Gell and Coombs with the modifications made to the previous classification are described in detail. Different types of hypersensitivities, their process, the contribution of various cells and molecules to normal immune responses and to hypersensitive reactions are discussed separately. The examples for different types of immune responses are described thoroughly to get a proper understanding of the topic. The clinical manifestations of different types of hypersensitivities and their means of prevention, evaluation and management are also depicted in separate chapters with clear insight. Lastly, the airborne allergens responsible for the allergy, different types of aeroallergens, their effects and allergies caused by them are described. The effect of climate change on aeroallergen production, various diagnostic tests for detection of aero-allergy with their prevention and control are discussed in detail separately. The book contains a reasonable number of diagrams, flowcharts and tables. Besides this, various interesting and self-explanatory illustrations are incorporated to make the book useful to the students for whom it is written. The question bank, which includes long answer type, short answer type and multiple choice questions with their answers at the very end of each chapter, is developed to get a full grasp of the topic.