The ideology of Thailand's left-wing radicals exerted a powerful force in the political turmoil of the 1970s. This ideology, which served as the rationale for the student uprising of 1973 that overthrew the military government weakened by the erosion of its credibility, was essentially the continuation of the fusion of Thai values with elements of Marxism first explored by intellectuals of an earlier generation. It was also the ideological basis for the reforms attempted by the left-wing political activists over the 1973-76 period. However, they met with strong resistance from those with vested interests who feared the adverse outcome of such socialist-inclined reform programmes, and organized countermeasures to suppress them. The ensuing period of turbulence bred mounting violence and extreme frustrations which compelled many radicals to flee into the jungle and join forces with the Communist Party of Thailand (CPT). Even as they confronted their common enemy, ideological differences and tactical disagreements between these radicals and CPT cadres soon emerged. The disputes came to a head in 1981 when most of the leaders left the CPT and surrendered themselves to the government authorities. Thai left-wing ideology, defined on one side by its oppo sition to the Thai Government and to the feudal values of traditional Thai society, gained further clarity and refinement through the forced contact and interaction with the communist ideology of the CPT. This study discusses the genesis of Thai radical ideology, its vicis situdes in the 1970s, its nature today, and its probable influence on Thai society in the future. The material presented is based on intensive interviews with 22 of the intellectuals and leaders who joined forces with the CPT between 1975 and 1981, and then left the armed struggle.1 The published writings of these individuals were also taken into account. Interviews with Thai security officials who conducted debriefing sessions with the returned radicals provide another perspective.