Using confidential Census data on U.S. manufacturing plants, we document that most of the dispersion in investment rates across plants occurs within firms instead of across firms. Between- firm dispersion is almost acyclical, but within- firm dispersion is strongly procyclical. To investigate the role of firms in the allocation of capital in the economy, we build a multi-plant model of the firm with frictions at both levels of aggregation. We show that external financing constraints at the level of the firm can have important implications for plant-level investment dynamics. Finally, we present empirical evidence supporting the predictions of the model.