Abstract
We provide characterizations of tacit collusion (simultaneous) equilibrium in models of investment timing allowing for spillovers in both áow proÖts and investment costs. We validate these characterizations by applying them to common models of capacity accumulation and R&D investment, as well as to investment in an endogenously priced input. For instance, in linear demand Cournot competition, tacit collusion is likelier to arise when installed capacities and lumpy investments are both large.