Legislative malapportionment is one of the main determinants of the partisan effects of electoral systems in democratic countries. Previous research has focused on determining the effects of malapportionment on elections results, in particular the overrepresentation of right-wing parties. By contrast, little effort has been devoted to the causes of malapportionment. Using an original dataset on legislative malapportionment in all countries of the world after 1945, we map the conditions under which malapportionment emerges in new democracies as a result of the strategic decisions of ruling elites. Two hypotheses on the determinants of legislative malapportionment in current democracies are explored. On the one hand, we expect malapportionment to be lower in case of a previous left-wing dictatorship. On the other hand, we expect malapportionment to be higher in case of top-down democratic transitions. In the final part of the paper, the existence of potential interactive effects between these two hypotheses is examined.