The modification of eukaryotic proteins by isoprenoid lipids, which is known as prenylation, controls the localization and activity of a range of proteins that have crucial functions in biological regulation. The roles of prenylated proteins in cells are well conserved across species, underscoring the biological and evolutionary importance of this lipid modification pathway. Genetic suppression and pharmacological inhibition of the protein prenylation machinery have provided insights into several cellular processes and into the aetiology of diseases in which prenylation is involved. The functional dependence of prenylation substrates, such as RAS proteins, on this modification and the therapeutic potential of targeting the prenylation process in pathological conditions accentuate the need to fully understand this form of post-translational modification.