Using a simple and graphical approach this atlas addresses themechanisms involved in the immune responses of dogs and cats, anddescribes the most important infectious and parasitic diseases, aswell as the corresponding preventive strategies. A particular emphasisis placed on pathological immune processes such as allergies,dermatitis, and possible adverse reactions to transfusions andvaccinations. This atlas is designed as an aid to veterinary surgeonswho wish to explain these important and complex concepts to petowners in simple but precise terms. This will help owners understandthe processes underlying the development of some of the mostimportant diseases of their pets, the immune defence mechanismsinvolved, and the importance of disease prevention throughimmunisation, ultimately aiding decision-making in specific cases.