Bey (/Bey, / Bek, / Beg or Beyg) is a Turkish title for chieftain, traditionally applied to the leaders (for men) of small tribal groups. The feminine equivalent title was Begum. The regions or provinces where "beys" ruled or which they administered were called beylik, roughly meaning "emirate" or "principality" in the first case, "province" or "governorate" in the second (the equivalent of duchy in other parts of Europe). Today, the word is still used informally as a social title for men (somewhat like the English word "mister" and the French word monsieur, which literally means "my lord"). Unlike "mister" however, it follows the name and is used generally with first names and not with last names.

Bey is the Turkish term for a tribal chieftain, Ottoman or later Islamic official, in latter days reduced to a hollow form of address; a leader of beylik.