Pathology is a branch of medicine, concerned with the study of disease in all aspects, namely nature, causes, development, and consequence. Examination of pathologic condition is divided into several subspecialties like, clinical, cellular pathologies. Medical pathology is divided in two main branches, anatomical pathology and clinical pathology. Veterinary pathology is concerned with animal disease, whereas phytopathology is the study of plant diseases. General pathology, also called investigative pathology, experimental pathology or theoretical pathology, is a broad and complex scientific field which seeks to understand the mechanisms of injury to cells and tissues, as well as the body’s means of responding to and repairing injury. Anatomical pathology, clinical pathology, forensic pathology, veterinary pathology, plant pathology, and molecular pathology are some important topics which are discussed thoroughly in this chapter.