Hatt-i Humayun may refer to:

• Hatt-i humayun, a handwritten note of an official nature by the Ottoman Sultan
• Hatt-i Humayun of 1856, also known as the "Reform Edict of 1856" (in Turkish: Islâhat Hatt-i Hümâyûnu or Islâhat Fermâni )

Hatt-i humayun (Ottoman Turkish: خط همايون, Turkish: hatt-ı hümayun or hatt-ı hümâyûn), also known as hatt-i sharif (hatt-ı şerîf), is the diplomatics term for a document or handwritten note of an official nature composed by an Ottoman sultan. The terms come from hatt (Arabic: handwriting, command), hümayun (imperial) and şerif (lofty, noble). These notes were commonly written by the Sultan personally, although they could also be transcribed by a palace scribe. They were written usually in response to, and directly on, a document submitted to the sultan by the grand vizier or another officer of the Ottoman government. Thus, they could be approvals or denials of a letter of petition, acknowledgements of a report, grants of permission for a request, an annotation to a decree, or other government documents. Hatt-ı hümayuns could be composed from scratch, rather than as a response to an existing document. After the Tanzimat reform (1856), aimed to modernize the Ottoman Empire, hatt-ı hümayuns of the routine kind were supplanted by the practice of irâde-i seniyye, in which the Sultan's spoken response was recorded on the document by his scribe.