According to firm lifecycle theory the agency costs of free cash flows are not transitory problems, but are a recurrent issue once firms reach a certain stage in their lifecycle. In particular, as firms mature their cash flows increase substantially while their investment opportunities decline and, to prevent retrenchment, managements need to invest in negative net present value projects. However, too much overinvestment leads to low firm valuation and potentially a hostile takeover. This paper extends firm lifecycle theory by arguing that to neutralize the threat of takeover, managements of maturing firms and their boards of directors progressively deploy antitakeover provisions which allow them to overinvest safely and prevent a decline in the size of their corporations. Firm lifecycle theory is also tested empirically. In this respect, a contribution of this paper is to develop a new empirical index that permits the identification of mature corporations with governance problems due to agency costs of free cash flows. The empirical results show that as firms mature agency costs of free cash flows increase, more antitakeover provisions are put into place and firms invest in projects with returns below their cost of capital.