The document provides methods for biosynthesizing isobutene using one or more isolated enzymes such as one or more of an enoyl-CoA dehydratase, a 2-hydroxyacyl-CoA dehydratase, an isovaleryl-CoA/acyl-CoA dehydrogenase and a mevalonate diphosphate decarboxylase, or using recombinant host cells expressing one or more such enzymes.