The idea that democracy fosters peaceful relationships among the nations is as old as at least the Kantian concept of perpetual peace, but in the twentieth century several new theories have been coined out in order to explain the behavior of democratic states towards other democracies and towards non-democratic states. These theories have been based on two interpretative models: structural/institutional and cultural/normative. This paper examines various versions of the democratic peace concept and places a particular attention at the explanatory power of the interpretative models and the role attached to the liberal values.