Type 1 diabetes is a multifactorial disease. Genetic predisposition and environmental factors favor the triggering of multiple autoimmune responses against pancreatic β cells; over time, chronic autoimmunity leads to severe β‐cell loss and an insulin‐dependent diabetic state for the life of the patient. Worldwide epidemiologic data show that the disease is more common in the Western world, especially among Caucasians of Northern European descent. There is a high level of clinical heterogeneity, both in disease progression, age of onset, and severity of clinical manifestations, possibly reflecting the interplay of diverse genetic and environmental factors on the severity and predominance of the pathogenic mechanisms leading to overt disease. Further studies to better assess the relative contributions of different pathogenic factors during disease progression are needed for a more integrated understanding of the disease pathogenesis.