Beginning in the mid-1980s, in the absence of active encouragement from the IMF’s management or member states, the staff began to encourage the liberalization of capital controls as a norm. This behavior constitutes a puzzle for the conventional wisdom, which sees the “Wall Street-Treasury Complex” as responsible for the IMF’s approach, as well as a blind spot for rationalist approaches, which offer little insight into processes that shape preference formation “from within” international organizations (IOs). In a context where the Fund’s member states permitted the staff considerable discretion and autonomy, I argue the staff’s initial adoption of the norm of capital freedom was largely shaped by three internal processes: administrative recruitment, adaptation, and learning. But norm adoption did not mean the end of internal discussion, and a vigorous debate emerged between “gradualists” and supporters of the “big bang” over how the norm should be interpreted and applied. In this “battle of ideas,” I emphasize the critical role of internal entrepreneurship.