I present a theory about the institutional determinants of democracy, arguing that the party system format is a central determinant of democracy. In turn, institutional engineering largely shapes the party system. Parliamentary systems and party list proportional representation are more conducive to a strong party system with competitive, programmatic and institutionalized political parties, and consequently to democracy. To show this, I look at a subset of post-Communist polities, those with a majority Orthodox population, thus controlling for the effect of religion. When we look at the relationship between economic development ( another important explanatory variable) and democracy, we see that in this group the relationship is actually negative. I offer an institutional explanation for this paradox: less economically developed Orthodox countries have made better institutional choices than more economically developed Orthodox countries.