The analysis of corporate governance has been a one-sided affair. The focus has been on “internal” accountability mechanisms, namely boards and shareholders. Each has become more effective since debates about corporate governance began in earnest in the 1970s but it is doubtful whether this process can continue. Correspondingly, it is an opportune time to expand the analysis of corporate governance. This article does so by focusing on three “external” accountability mechanisms that can operate as significant constraints on managerial discretion, namely governmental regulation of corporate activity, competitive pressure from rival firms and organized labor. A unifying feature is that each was an element of a theory of “countervailing power” economist John Kenneth Galbraith developed in the 1950s with respect to corporations, an era when external accountability mechanisms did more than their internal counterparts to keep management in check.