The formal rules governing the UN Security Council offer little insight into how negotiations are conducted on a day-to-day basis. While it is generally assumed that permanent members dominate negotiations, this article investigates avenues for influence for elected members and the UN Secretariat. Institutional power is used to show how permanent members adopt dominant positions in negotiations extending far beyond their Charter-given privileges. Dominance of permanent members is moderated, however, by the legitimacy that support from elected members brings to a resolution. Similarly, the UN Secretariat can use its legitimated authority to influence decisions. The article argues that informal practices are key in understanding how power and influence are allocated in the Council and it forms a building block for future analyses of Security Council practices. This argument also has implications for the perennial reform debates and the prospects for informal reform.