Bioluminescence, the conversion of chemical energy into light in living organisms, is dependent on two principal components, an enzyme luciferase and the substrate luciferin. Light emission occurs in many different species in phylogenetically diverse organisms with estimates that bioluminescence may have arisen independently as many as 50 times in the course of evolution. In beetles only a small percentage of species are luminescent and most are found in three coleopteran families within the superfamily Elateroidea; the Lampyridae (fireflies and glow-worms), the Phengodidae (railroad worms) and the Elateridae (click beetles). The enzyme responsible for bioluminescence in beetles, firefly luciferase, is highly conserved between families, although changes in amino acid residues can impact on the colour of the light emitted. It has been hypothesised that luciferase evolved from a fatty acyl-CoA synthetase gene deriving a novel bioluminescent function (neofunctionalization) after a gene duplication event. Recent phylogenetic studies have shown extensive gene duplication of luciferase within the Coleoptera and luciferase-like genes driving the hypothesis that beetle luciferase may have arisen from a process of subfunctionalization as opposed to neofunctionalization early on in Elateroidea evolution. The impact of gene duplication on shaping the evolution of bioluminescence is further highlighted in the colour of light emitted by bioluminescent beetles. Recent evidence has shown that intergenic exchange between duplicated luciferase loci is common in some members of the Elateridae. Furthermore, gene flow and intergenic exchange shuffled substitutions have given rise to new colour phenotypes in Jamaican click beetles. Herein is presented a review on the evidence for functional divergence of duplicated luciferase genes in bioluminescent beetles that have given rise to the first luminescent beetles and the evolution of bioluminescent colour.