© The Author(s) 2018. Published by Oxford University Press on behalf of The Society for Financial Studies. All rights reserved. We study time-series and cross-firm variation in corporate cash holdings from 1920 to 2014. The recent increase in cash is not unique in magnitude. However, the recent divergence between average and aggregate cash is new and entirely driven by a shift in cash policies of newly public firms, whereas within-firm changes have been negative or flat since the 1940s. Cross-sectional relations between cash holdings and firm characteristics are stable throughout the century, though characteristics explain little of the trends in aggregate cash. Macroeconomic conditions, corporate profitability and investment, and (since 2000) repatriation taxes explain aggregate cash over the last century.