Ethylidene norbornene (ENB) is an organic compound that consists of an ethylidene (CH3C(H)=) group attached to norbornene.

The compound consists of (E)- and (Z)-stereoisomers, but the mixtures are typically not separated.

It is prepared by isomerization of vinyl norbornene, which in turn is obtained by the Diels-Alder reaction of butadiene and cyclopentadiene.

[1] It is a monomer that used in the production of the commercial polymer EPDM.

The exocyclic double bond (the ethylidene group) undergoes sulfur vulcanization.