ENThe nationalities factor in Soviet politics received little attention from scholars until the Soviet Union was on the verge of disintegration. Studies that examined popular mobilization and politics outside Moscow generally focussed on the emergence of informal groups and "civil society," failing to note that the primary competitors to the Communist Party were almost always ethnically-based movements. To understand the origins of Gorbachevera ethnopolitical mobilization, I explore how Soviet policy institutionalized ethnicity and used it as an important criterion in the distribution of socioeconomic rewards and opportunities, political power, and status. To understand the timing of the nationality explosion, I explore how policy changes wrought by Andropov and Gorbachev undermined incentives for non-Russians to work within the system and created new opportunities for mobilization "from below." After explaining the emergence of the broad "wave" of ethnopolitical mobilization, I focus on the Estonian, Latvian, and Lithuanian popular movements, which posed the most sustained challenge to Moscow and served as models and catalysts for movements in other republics. I find the impetus for Baltic mobilization in the perception of imminent threats to group boundaries and cultural values, a desire to highlight the illegitimacy of the legacy of World War II, and discontent with ethnic inequality imposed by the regime. Splits and disarray in the central and Baltic political elites created the conditions for the emergence of the popular movements and the rapid surge of mobilization after the summer of 1988.I explore the concerted efforts of the Balts to "export their revolutions" elsewhere in the Soviet Union and argue that they were motivated by both ideology and a desire to gain allies for struggles against Moscow and opponents of change within the Baltic republics. In assessing the all-Union impact of Baltic politics, I find that other movements emulated or were inspired by the "Baltic model." Moreover, I find that the Balts played an important role in precipitating the final nationalities crisis of the Soviet Union: the August coup and the disintegration of the country along republican lines. The research for this dissertation includes interviews with leaders of the Baltic movements and a thorough review of the official and unofficial press. In a broad sense, this dissertation addresses the role of ethnicity in soviet politics before and during the Gorbachev era. In a narrower sense, this dissertation explains why ethnopolitical mobilization in the Baltic republics was so extensive and influential.