Mahmud II (Ottoman Turkish: محمود ثانى, romanized: Mahmud-u s̠ānī, Turkish: II. Mahmud; 20 July 1785 – 1 July 1839) was the 30th Sultan of the Ottoman Empire from 1808 until his death in 1839.

His reign is recognized for the extensive administrative, military, and fiscal reforms he instituted, which culminated in the Decree of Tanzimat ("reorganization") that was carried out by his sons Abdulmejid I and Abdülaziz. Often described as "Peter the Great of Turkey", Mahmud's reforms included the 1826 abolition of the conservative Janissary corps, which removed a major obstacle to his and his successors' reforms in the Empire. The reforms he instituted were characterized by political and social changes, which would eventually lead to the birth of the modern Turkish Republic.Notwithstanding his domestic reforms, Mahmud's reign was also marked by nationalist uprisings in Ottoman-ruled Serbia and Greece, leading to a loss of territory for the Empire following the emergence of an independent Greek state.

In the general structure of the Ottoman Empire, Mahmud's reign was characterized by showing major interest to Westernization; institutions, palace order, daily life, clothing, music and many other areas saw radical reform as the Ottoman Empire opened up to the modernisation.