This chapter presents a state of the art summary of multiple endocrine neoplasia (MEN) in relation to its biology, epidemiology, disease mechanisms, clinical signs, diagnosis, treatment and prognosis. Based on the specific genes involved, types of hormones made, and characteristic signs and symptoms, MEN is distinguished into MEN type 1, MEN type 2A, MEN type 2B, and MEN type 4. MEN represents a group of autosomal dominant tumor predisposition syndromes that target the endocrine system. MEN1 has an estimated prevalence of 2–20 cases per 100,000. Inherited in an autosomal dominant pattern, MEN1 shows a high degree of penetrance, with biochemical signs detected in greater 95% and clinical signs in 80% of patients by the fifth decade of life. MEN1 is linked to more than 20 endocrine and non-endocrine tumors. A combination of family history, clinical features, biochemical tests, and genetic detection is utilized for MEN diagnosis.