Although the UN Development System may not command the largest budgets, it wields outsized influence by shaping the norms, priorities and legitimacy of multilateral cooperation. Beneath its formal machinery—boards, committees and mandates—decisions increasingly hinge on informal networks of power, the financial clout of major donors and unequal access to decision-making. This report charts where authority really lies within the UN Development System, exposes how governance functions in practice, and explains why these entrenched dynamics are eroding its legitimacy just as UN reform reaches a pivotal moment.