This study analyses the heterogeneity in the speed of capital structure adjustment. Using a doubly-censored Tobit estimator that accounts for mechanical mean reversion in leverage ratios, the speed of adjustment is 25\% per year in a large international sample, supporting the economic relevance of the trade-off theory. Differences in the adjustment speed across financial systems are attributable to differences in the costs of adjustment. Macroeconomic and micro-level supply-side constraints also affect the dynamics of leverage. Firms adjust more slowly during recessions, and the business cycle effect on adjustment speed is most pronounced for financially constrained firms in market-based countries.