Veterinary disease refer to an impairment that leads to a modification in the vital functions of animals. These diseases are an important area of study as they affect the economy and may transmit the causative agents to the humans. There are several reasons which have been cited for the spread of diseases, like poor sanitation, nutritional defects, pathogenic defects, improper management, etc. Pathogenic defects include certain organisms that produce toxins and harmful elements that upset the metabolic activity of animals. Viruses and bacteria are the most common disease-causing agents. They are microscopic and multiply rapidly under favorable conditions. Other pathogenic causative agents include fungi and protozoans. These pathogens live inside or outside the animal's body and alter vital functions by suppressing their immune system. This book unfolds the innovative aspects of pathological basis of veterinary disease which will be crucial for the progress of this field in the future. It will also provide interesting topics for research which interested readers can take up. Scientists and students actively engaged in this field will find this book full of crucial and unexplored concepts.