Mu'in al-Din or Moinuddin (Arabic: معین الدین) is a male Muslim name composed of the elements Muin, meaning helper and ad-Din, meaning of the faith.[1][2] It may refer to:
- Mu'in ad-Din Unur (d. 1149), Seljuk ruler of Damascus
- Mu'in al-Din Chishti (1143–1236), Sufi saint
- Mu'in al-Din Hasan ibn al-Shaykh (d. 1246), vizier of the Ayyubid sultanate
- Pervâne Mu'in al-Din Suleyman (d. 1277), politician in Anatolia
- Mo'in al-Din Junayd ibn Mahmud ibn Muhammad Baghnovi Shirazi, or just Junayd Shirazi (fl. 1389), Persian Sufi poet
- Muhammad Mueenuddeen I (d. 1835), sultan of the Maldives
- Muhammad Mueenuddeen II (fl. 1887), sultan of the Maldives
- Moinuddin Haider (b. 1942), Pakistan army General
- Moinuddin Aqeel (b. 1946), Pakistani author, critic and linguist
- Mirza Ghulam Moinuddin Muhammad, Javaid Jah Bahadur (b. 1946), Indian descendant of the Mughal emperors
- Moin al-Din Saeedi , Baluchi-Iranian Politician
- Moinuddin (cricketer) (b. 1987), Pakistani cricketer