Shāh (/ˈʃɑː/; Persian: شاه‎, [ʃɒː]) is the title of the ruler of certain South Asian and Central Asian countries, especially Persia (modern Iran), and derives from the Persian word shah, meaning "king".

Shah or shahanshah ("King of Kings") was the title of Persian emperors or kings. It includes rulers of the first Persian Empire, the Achaemenid dynasty, who unified Persia and created a vast intercontinental empire, as well as rulers of succeeding dynasties. The title was also extensively used later by emperors of the Indian subcontinent, including those of the Mughal Empire. For instance, the third Mughal emperor, Akbar the Great (1542–1605), was formally known as "Shahanshah Akbar-e-Azam".

The full title of the Achaemenid rulers was Kshatriya Kshatriyanamah, "King of Kings" in Old Persian, corresponding to Middle Persian šāhān šāh, literally "kings' king", and Modern Persian shāhanshāh (شاهنشاه).^{[citation needed]} In Greek, this phrase was translated as "βασιλεύς τῶν βασιλέων (basileus tōn basiléōn)", "king of kings", equivalent to emperor. Both terms were often shortened to their roots: shah and basileus.