Why do the reported effects of privatization on firm performance vary so much? This paper provides new estimates of these effects and tests potential explanations for heterogeneity using comprehensive, long-panel data for 70,000 firms in five East European economies. We estimate that privatization raises measures of profitability, productivity, and growth by about 5–12% on average, but with substantial variation across countries and time periods. Analyzing heterogeneity in privatization effectiveness, we find little systematic role for firm size, financial dependence, exchange listing, or technological complexity, but important variation by fraction privatized, ownership concentration, firm quality, and the macroeconomic and institutional environment.