A genetically modified host cell capable of producing an isoprenoid and comprising: a) (i) a coding region comprising a nucleotide sequence encoding a mevalonate kinase; a nucleic acid comprising a nucleotide sequence encoding one or more mevalonate pathway enzyme other than MK, wherein the copy number of coding regions comprising nucleotide sequences encoding the MK is higher than the copy number of coding regions encoding the one or more mevalonate pathway enzyme other than MK; and (ii) a heterologous nucleotide sequence encoding a terpene synthase; or b) (i) a coding region encoding a MK, wherein the MK coding region is under the control of a first promoter; (ii) a nucleic acid comprising a nucleotide sequence encoding one or more mevalonate pathway enzyme other than mevalonate kinase under the control of a second promoter wherein the second promoter is weaker than the first promoter within said host cell; and (iii) a heterologous nucleotide sequence encoding a terpene synthase; wherein, in the case of (a) or (b) above, the level of MK produced in said host cell is at least 50% higher than the level of the one or more mevalonate pathway enzyme other than MK and said mevalonate pathway enzyme other than MK is selected from acetoacetyl-CoA thiolase, hydroxymethylglutaryl-CoenzymeA (HMG-Co) synthase (HMGS), HMG-CoA reductase (HMGR), phosphomevalonate kinase, and mevalonate pyrophosphate decarboxylase. a) (i) a coding region comprising a nucleotide sequence encoding a mevalonate kinase; a nucleic acid comprising a nucleotide sequence encoding one or more mevalonate pathway enzyme other than MK, wherein the copy number of coding regions comprising nucleotide sequences encoding the MK is higher than the copy number of coding regions encoding the one or more mevalonate pathway enzyme other than MK; and (ii) a heterologous nucleotide sequence encoding a terpene synthase; or (i) a coding region comprising a nucleotide sequence encoding a mevalonate kinase; a nucleic acid comprising a nucleotide sequence encoding one or more mevalonate pathway enzyme other than MK, wherein the copy number of coding regions comprising nucleotide sequences encoding the MK is higher than the copy number of coding regions encoding the one or more mevalonate pathway enzyme other than MK; and (ii) a heterologous nucleotide sequence encoding a terpene synthase; b) (i) a coding region encoding a MK, wherein the MK coding region is under the control of a first promoter; (ii) a nucleic acid comprising a nucleotide sequence encoding one or more mevalonate pathway enzyme other than mevalonate kinase under the control of a second promoter wherein the second promoter is weaker than the first promoter within said host cell; and (iii) a heterologous nucleotide sequence encoding a terpene synthase; (i) a coding region encoding a MK, wherein the MK coding region is under the control of a first promoter; (ii) a nucleic acid comprising a nucleotide sequence encoding one or more mevalonate pathway enzyme other than mevalonate kinase under the control of a second promoter wherein the second promoter is weaker than the first promoter within said host cell; and (iii) a heterologous nucleotide sequence encoding a terpene synthase;