The Treasury inspires fascination and sometimes envy in British government but we know very little about what it is like to work in it or deal with it. Its role at the centre of economic policy is familiar, but it also has a major influence on social policy through its control of the purse and its constant dialogue with spending departments.This important new study draws upon extensive in-depth interviewing inside the Treasury and the rest of Whitehall. The authors show how the Treasury has been winning the contest for control of welfare strategy, especially under New Labour. In recent years the Treasury has undergone major internal changes and as part of that process officials have tried to change their style of behaviour towards Whitehall colleagues. The progress of these reforms is captured in the words of officials in both the Treasury and other departments.