Bey (Ottoman Turkish: بك, romanized: beğ, Turkish: bey, Azerbaijani: bəy, Turkmen: beg, Uzbek: бек, Kazakh: би/бек, Kyrgyz: бий/бек, Tatar: бәк, romanized: bäk, Shor: пий/пек, Albanian: beu/bej, Serbo-Croatian: beg, Persian: بیگ, romanized: beyg/beig, Tajik: бек, Arabic: بك, romanized: bēk) is a Turkic title for a chieftain, and an honorific, traditionally applied to people with special lineages to the leaders or rulers of variously sized areas in the numerous Turkic kingdoms, emirates, sultanates and empires in Central Asia, South Asia, and the Middle East, such as the Ottomans, Timurids or the various khanates and emirates in Central Asia and the Eurasian Steppe. The feminine equivalent title was begum. The regions or provinces where "beys" ruled or which they administered were called beylik, roughly meaning "governorate" and/or "region" (the equivalent of county in other parts of Europe). However the exact scope of power handed to the beks (alternative spelling to beys) varied with each country, thus there was no clear-cut system, rigidly applied to all countries defining all the possible power and prestige that came along with the title.

Today, the word is still used formally as a social title for men, similar to the way the titles "sir" and "mister" are used in the English language. Additionally, it is widely used in the naming customs of Central Asia, namely in countries such as Uzbekistan, Tajikistan, Kazakhstan and Kyrgyzstan. Notably, the ethnic designation of Uzbeks comes from the name of Öz Beg Khan of the Golden Horde, being an example of the usage of this word in personal names and even names of whole ethnic groups. The general rule is that the honorific is used with first names and not with surnames or last names.