This paper examines the factors influencing leverage decisions of publicly traded American firms from 1950 to 2003. The authors identify six core factors that reliably predict leverage: median industry leverage, market-to-book ratio, tangibility, profits, log of assets, and expected inflation. These factors are consistent across different definitions of leverage and show reliable empirical patterns. The study also finds that the importance of these factors has changed over time, with profits becoming less significant in recent years. The findings support some versions of the tradeoff theory of capital structure, which posits that firms balance the costs and benefits of debt financing. The paper discusses the implications of these findings for various capital structure theories, including the tradeoff theory, pecking order theory, and market timing theory.This paper examines the factors influencing leverage decisions of publicly traded American firms from 1950 to 2003. The authors identify six core factors that reliably predict leverage: median industry leverage, market-to-book ratio, tangibility, profits, log of assets, and expected inflation. These factors are consistent across different definitions of leverage and show reliable empirical patterns. The study also finds that the importance of these factors has changed over time, with profits becoming less significant in recent years. The findings support some versions of the tradeoff theory of capital structure, which posits that firms balance the costs and benefits of debt financing. The paper discusses the implications of these findings for various capital structure theories, including the tradeoff theory, pecking order theory, and market timing theory.