◢ On Monday, the Iranian rial sank to a historic low. But those Iranians who scrambled to convert their rials into dollars found it difficult to do so—as they have for months. This important detail of the current crisis has gone largely unexamined. While the determinants for demand for foreign exchange are well understood, the second determinant of market prices—foreign exchange supply—remains subject to mere passing mention. This is a mistake. Iran’s currency crisis is a supply-side story.