Pure humulene is shown to be 1,1,4,8-tetramethylcycloundeca-3,7,10-tree. The present results also demonstrate that Chapman's humulene has this structure. On the other hand, the structures proposed for humulene by Sorm et al. (1949, 1952) and by Fawcett and Harris (1954a, 1954b, 1954c) are incorrect.