We analyze the main rationale for public administrations and political institutions for supplying transparency, namely, that it generates legitimacy for these institutions. First, we discuss different theories of decision making from which plausible causal mechanisms that may drive a link between transparency and legitimacy may be derived. We find that the common notion of a straightforward positive correlation is naïve and that transparency reforms are rather unpredictable phenomena. Second, we test the effect of transparency on procedure acceptance using vignette experiments of representative decision making in schools. We find that transparency can indeed generate legitimacy. Interestingly, however, the form need not be “fishbowl transparency,” with full openness of the decision-making process. Decision makers may improve their legitimacy simply by justifying carefully afterward the decisions taken behind closed doors. Only when behavior close to a deliberative democratic ideal was displayed did openness of the process generate more legitimacy than closed-door decision making with postdecisional justifications.