We use book translations as a new measure of international idea flows and study the effects of Communism’s collapse in Eastern Europe on these flows. Using novel data on 800,000 translations and difference-in-differences approaches, we show that while translations between Communist languages decreased by two thirds with the collapse, Western-to-Communist translations increased by a factor of five and quickly converged to Western levels. Convergence was more complete in more economically-useful fields such as the sciences, and was more complete in Satellite than in Soviet countries. These findings help us understand how institutions shape the international diffusion of knowledge.