E40 may refer to:

• Nimzo-Indian Defense, Encyclopaedia of Chess Openings code
• European route E40, a road extending from France to Kazakhstan
• E-40 (born 1967), American rapper
• GE E40, a locomotive
• E40, the name for the fuel blend of 40% ethanol and 60% gasoline
• E40 screw, a type of Edison screw
• HMS E40, a 1916 British E class submarine

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