Abstract: | This paper makes two arguments. First, the political and economic institutions of a state affect that state's foreign policy preferences. Second, dyads with similar political and economic institutions are less likely to experience conflict than other types of dyads. After developing the logic of these arguments, I create measures of political and economic institutional similarity and test the hypotheses against the empirical record. The empirical analysis supports the argument that dyadic institutional similarity reduces the likelihood of conflict. The most noteworthy finding is that economic institutional similarity, even when the political institutions in a dyad are dissimilar, reduces the likelihood of militarized conflict. |