The Treaty of Daan (or Da'an) was an agreement signed on 9 October 1911 at Daan in the Yemen Vilayet by a representative of the Sultan of the Ottoman Empire and Imam Yahya Muhammad Hamid ed-Din, the Zaydi Imam of Yemen expanding autonomy in the Ottoman province.
Imam Yahya was the spiritual and temporal leader of the Zaydi branch of Shi'a Islam in Yemen. According to the treaty, the imamate (Zaydi-controlled areas) was to be governed by sharia law and the imam was given the power to appoint governors and judges, as well as collect taxes, while remaining under Ottoman authority.
The Ottoman government came to this decision after years of Zaydi-based insurgency in Yemen; the treaty had been suggested as early as 1906 by a delegation of ulema from Mecca.
After the collapse of the Ottoman Empire in 1918, Iman Yahya became King of the now independent Mutawakkilite Kingdom of Yemen.