E91

E91 may refer to:
 * E91 protocol, a protocol of Quantum Cryptography
 * E91, a car of the BMW 3 Series
 * King's Indian Defense, Encyclopaedia of Chess Openings code
 * European route E91, one of the many routes in the European route network.
 * Minami-Hanna Road and Yamatotakada Bypass, route E91 in Japan.