MEK or Mek may refer to:
- Methyl ethyl ketone (butanone), a solvent, used also to weld some plastics
- Mujahideen-e Khalq, the Iranian organization known in English as the People's Mujahedin of Iran
- MEK Compound, in Fallujah, Iraq, a large compound used by the U.S. military from 2003 to 2009
- Mek (comics), a comic mini series by Warren Ellis
- Magyar Elektronikus Könyvtár, or the Hungarian Electronic Library, a digital library
- Message Encryption Key, a type of key in cryptography
- Mobiles Einsatzkommando, a special police unit in Germany
- Mitogen-activated protein kinase kinase
- Mek people, an indigenous tribe of West Papua, Indonesia
- Mek languages, a family of Papuan languages spoken by the Mek peoples
- Mu Epsilon Kappa Society, an organization of anime clubs
- Mek, the title held by rulers of the Sultanate of Sennar