Pathology is the study of abnormal and unhealthy processes and states of health, including their causes. Research addresses isolated phenomena (symptoms) as well as associations of symptoms (syndromes) and all kinds of abnormalities. Pathology studies the causes (aetiology), the origin (pathogenesis), the evolution and effects of diseases, and the different physiological processes (functional pathology, or pathophysiology).
Pathological diagnosis, i.e. the activity carried out by the pathologist (the specialist in pathology), is primarily based on the analysis of tissues through their macroscopic appearance (pathological anatomy) and optical microscopic appearance (histopathology, cytology). Biochemical and molecular biology methods are used more and more frequently, as is electron microscopy in the field of research. Pathologists also perform clinical autopsies. However, the examination of tissues from living patients (biopsy) is much more common.