The so-called Isan issue in Thailand is related not only to the economic, but also cultural conflict between the northeastern (Isan) region and the central government. The Thai government has been since 1960s trying to integrate the Isan region into the nation-state of Thailand, particularly by promoting economic development in that region. However, the policy of integration which has been pursued since just a few decades is merely a political approach to the Isan problem which has a complex background. The Isan problem is to be understood against the background of political, economical, and cultural relations between the northeastern people, largely Lao, and the Central Thai (Siamese) which have a history of several centuries. More importantly, through the relations has developed the Isan identity, which has two faces - the Isan regional identity and the Thai national identity. Key Words：Northeast Region, Isan Identity, Regionalism.