Abstract: The desirability of a dual-class structure, which enables founders of public companies to retain a lock on control while holding a minority of the company's equity capital, has long been the subject of a heated debate. This debate has focused on whether dual-class stock is an efficient capital structure that should be permitted at the time of initial public offering ("IPO"). By contrast, we focus on how the passage of time since the IPO can be expected to affect the efficiency of such a structure. Our analysis demonstrates that the potential advantages of dual-class structures (such as those resulting from founders' superior leadership skills) tend to recede, and the potential costs tend to rise, as time passes from the IPO. Furthermore, we show that controllers have perverse incentives to retain dual-class structures even when those structures become inefficient over time. Accordingly, even those who believe that dual-class structures are in many cases efficient at the time of the IPO should recognize the substantial risk that their efficiency may decline and disappear over time. Going forward, the debate should focus on the permissibility of finite-term dual-class structures -- that is, structures that sunset after a fixed period of time (such as ten or fifteen years) unless their extension is approved by shareholders unaffiliated with the controller. We provide a framework for designing dual-class sunsets and address potential objections to their use. We also discuss the significant implications of our analysis for public officials, institutional investors, and researchers.