We investigate investment behavior when there is asymmetry of information between owners (the principal) and managers (the agent). The model accepts the standard cost-of-adjustment model as a particular case and is directly compared with it. For all types, information asymmetry distorts the relationship between investment and the cost of capital, and the relationship between investment and the shadow value of capital. In particular, a regime of inaction appears over a certain cost range, in an observationnally different way than when fixed adjustment costs, or irreversibilities, cause a similar phenomenon. Uncertainty, in the form of an increase in the spread of agents' types, tends to reduce investment despite symmetric adjustment cost and perfect competition. The model clarifies the interpretation of Tobin's q under asymmetric information and explains some results of the mergers and acquisition literature.