This paper analyzes the voting behavior of Euro-parliamentarians. The roll call data from the plenary sessions of European parliament(EP) during the third and fourth legislatures is used to estimate legislators' preferences. Applying the spatial models of roll call voting to the EP, we investigate the dimensions underlying legislators' voting behavior. We focus on the relative importance of political party affiliation(i.e. ideology) versus nationality(i.e. the economic interest) as the main factor influencing the voting behavior. The results support the existence of a European political system where the main actors are political groups and not the delegations of nations. Also, the pattern of voting in the EP is found to be quite stable across time and issues. Moreover, after taking into account members' political party affiliations, nationality becomes, though to a lesser extent, statistically significant in explaining legislators' ideal positions.
