Existing theories of public sector entrepreneurship lack a sense of entrepreneurial discovery ubiquitous in human action. Instead, existing theories emphasise rational calculation in a public sector setting. Existing theories of public sector entrepreneurship, therefore, are inadequate to account for the observed entrepreneurial behaviour in political and bureaucratic settings. The purpose of this paper is to redress the limited theories of public sector entrepreneurship by integrating Kirznerian and Schumpeterian theories of entrepreneurship with Buchanan and Tullock's constitutional political economy to move toward a theory of public sector entrepreneurship. The following analytic definition is offered: public sector entrepreneurship occurs whenever a political or governmental actor is alert to, and acts on, potential political profit opportunities, thus equilibrating the policy subsystem in which the actor is embedded and moving it toward a new equilibrium.