The Iranian banking industry remains completely regulated by sharia law and is by far the world’s largest center of Islamic banking. Yet its experience is unique within the global Islamic community, as it is inspired by Shia jurisprudence, which often diverges from mainstream Sunni jurisprudence. Sunni scholars have repeatedly questioned the “rightfulness” of Iranian banks. However, with Iran now seemingly closer than ever to an agreement with the West over its controversial nuclear development program, local financial institutions are poised to regain access to international markets and place their sharia-compliant products among emerging market enthusiasts. Yet instead of adding new momentum to the growing Islamic finance industry, Iran’s financial comeback risks opening a new chapter in the century-old clash of principles between Sunni and Shia Islam.