Tuberous sclerosis complex (TSC) is a genetic disease caused by mutations in either the TSC1 or TSC2 gene. Mutations in TSC1 and TSC2 are responsible for approximately 30% and 60% of TSC cases, respectively. TSC is characterized by the development of benign hamartomas in many organs, including brain, kidney, heart, skin, and eyes. TSC hamartomas rarely develop to malignancy and are a mass of disorganized but differentiated cells originated from many different cell types. Major clinical symptoms include seizure, mental retardation, kidney failure, and lung dysfunction. Currently, there is no cure for TSC. Studies of TSC patients and animal models support the hypothesis that TSC1 and TSC2 are tumor suppressor genes and inhibit cell growth. TSC1 and TSC2 proteins form a complex and inhibit the function of Rheb, which is a positive cell growth regulator. Our main goal is to understand how the TSC1/TSC2 complex and Rheb are regulated in the cell and how these proteins control cell growth.