IN THIS PAPER we analyze the way that a firm which operates under uncertainty will behave during the current period and over time. To do so, we develop a new multi-stage model of the firm which has-as we show belowinteresting implications both for economic theory and for econometric research. The paper's main results are summarized in two theorems in Section 2. The first of these theorems shows that an entrepreneur who operates under uncertainty will behave in each period as if he were attempting to maximizesubject to production and financial constraints-a strictly concave one-stage objective function whose arguments represent: (1) the dividends which the firm pays during the period, and (2) the firm's end-of-period asset-and-financing structure. The second theorem shows that, if it is possible to represent the behavior over time of prices and certain other parameters by random processes, then the firm's behavior over time (as reflected during each period in the inputs it uses, the output it produces, the dividends it pays, and the end-ofperiod asset-and-financing structure it selects) can also be represented by well-defined random processes. The proofs of both theorems are given in the Appendix.