This article analyses the origins and consequences of multicameral representation and voting in international organizations. It is argued that the existence of visible and durable conflicts in an issue area can make standard procedures such as unicameral majority voting ineffective with respect to the functioning of the regime. Applying spatial models of strategic decision making, it is asserted that multicameralism is more likely to be effective than unicameralism if chambers consist of key groups with distinct interests. Empirical evidence is provided by studying the multicameral voting rule in the Council of the International Seabed Authority (ISA). I compare likely decision-making outcomes under unicameral and multicameral voting rules from 1996 to 2002 and find that multicameral outcomes are more likely to be stable and supported by those actors critical for the effective functioning of the regime.