Thai business group growth is stifled because of family business 1 entanglements. Although family business groups (FBGs) enabled Thailand to escape the low-income trap and achieve upper-middle-income status during the catch-up developmental period, in recent decades they became a key obstacle to attaining high-income status. Adopting an Anglo-American corporate governance style did not result in separation of ownership and control, or lead to a rise in professional managers and managerial enterprises. Tunnelling and minority shareholder expropriation persist.This chapter examines tunnelling and minority shareholders expropriation, a weakness of Asian corporate governance. Case studies in Thailand show a three-part family business trap: lack of separation between ownership and control, concentrated ownership (holding companies and cross shareholding), and sluggish managerial enterprise development. This chapter provides evidence of the emergence of managerial enterprise in Thailand, particularly in commercial banking, which transformed significantly during the 1997 Asian financial crisis, and in family businesses, which evolved into the fourth generation and attempted to modernize.