The Transatlantic Trade and Investment Partnership between the European Union and the US is highly technical. Still, the negotiations triggered large-scale protests among citizens with very diverse socioeconomic backgrounds. Why has a complex issue such an enormous mobilizing effect although the economic consequences are either unclear or favorable for the participating economies? We argue that the transparency of negotiations is an important consideration for people evaluating the negotiation outcome. Conducting a survey experiment, we show that non-transparent decision-making decreases citizens' appraisal of the agreement independent of its outcome: A non-transparent negotiation is, on average, almost 16 percent less likely to find public approval than a transparent but otherwise identical agreement. Our findings have important implications for democratic decision-making.
