a b s t r a c tThe separation of control and ownership -the ability of a small group effectively to control a company though holding a minority of its cash flow rights -is common throughout the world, but also is commonly decried. The control group, it is thought, will use its position to consume excessive amounts of the firm's returns, and this injures minority shareholders in two ways: there is less money and the controllers are not maximizing firm value. To the contrary, we argue here that there is an optimal share of the firm that induces the control group to maximize shareholder value while inducing investors to fund the firm's projects. The concern that controlled companies raise is that the controlling group cannot easily commit not to consume more than the optimal share. A firm's cost of capital is increasing in the controllers' inability to solve this credibility problem because potential investors will charge the firm for later consuming private benefits. Today, accurate judicial review of controlled transactions under mandatory fiduciary rules helps controllers to commit not to take more than the optimal share. Private contracting and judicial review are strong complements, however. Therefore, our principal normative recommendation is to open up the contracting space by reducing the fiduciary rules to defaults. This reform would be less helpful in developing countries that lack effective legal systems. The public corporations in such countries, however, also have controlling shareholders. We explore various non-legal methods by which these shareholders credibly commit to cap private benefits, although we also show that these methods are less efficient in a mature legal system than contracting would be.