This paper studies the impact of the competition between lobbies and voters on policy outcomes under alternative legislative procedures. Lobbies and citizens have opposing interests in a public policy and offer money and votes, respectively, to legislators to obtain their preferred policy. Comparing a unicameral and a bicameral legislative procedure, we show that bicameralism improves legislators' accountability when the same party controls the two chambers but not necessarily, if the two chambers are controlled by opposite parties. We also show that bicameralism with amendment rights (open rule) is better than bicameralism without amendment rights (closed rule). Finally, the evidence from a cross-country analysis, including 43 democracies, is consistent with our theoretical findings.