Drawing on a database for 1988–2006 containing information on 157 countries, we investigate the effects on military spending of government form and democracy, electoral rules and concentration of parliamentary parties. From an OLS regression on pooled data, our results show that presidential democracies spend more than parliamentary systems on defense, whereas its interaction with a majoritarian electoral rule reduces the defense burden. Our findings suggest that, in contrast to theoretical predictions in the literature, institutions do not have the same impact on the provision of all public goods.