This paper presents an equilibrium model in which the process of firm formation and technology adoption is endogenous. Individuals decide whether to work in an existing firm for a posted wage, or to establish a new firm. Entrepreneurs hire a single worker and choose a production technology from a fixed set. The stochastic properties of different technologies are known with different, and exogenously specified, degrees of precision. We use Dempster's (967) lower probabilities to characterize these differences in objective precision of risk information. Individuals in the model are heterogeneous with respect to their tolerance of imprecise risk. This heterogeneity determines which technologies are adopted in equilibrium, the number of firms adopting each active technology, firm structure (risk attitudes of owner and worker), and the wage differentials across firms adopting different technologies. We can also parametrically alter the risk precision associated with a given technology to examine the effect on equilibrium. This comparative static exercise suggests an explanation for the commonly observed S-shaped diffusion profile for successful innovations.