Approximately one-third of the world's countries have bicameral legislatures, that is, legislatures that involve two distinct chambers in their deliberations. These bicameral legislatures are not merely relics of longforgotten constitutional compromises. Although many of them have long constitutional histories, a number of newly forged constitutions, in Central Europe and Latin America in particular, also provide for dual legislative bodies. But there is surprisingly little agreement on the actual impact of bicameral institutions. As the quotations cited above suggest, bicameralism has both advocates and opponents. In this book, we address the debate and examine the effect of bicameral institutions on political outcomes.

The existence of a second chamber appears to have little effect on the relationship between the legislature and the executive. In presidential systems, the executive is elected directly and does not need the political support of the legislature to survive. In parliamentary systems, where the government needs the political support of the parliament to survive, this support is measured almost exclusively in the popularly elected lower chamber. Consequently, the relationship between legislative and executive is rarely altered directly by the existence of a second chamber.