In spite of millions of years of evolutionary divergence, the conservation of gene function is common across distant lineages. As such, genes that are known to influence behaviour in one organism are likely to influence similar behaviours in other organisms. Recent studies of the evolution of behaviour and morphological adaptation support this notion. Thus, the candidate gene approach offers great potential to expand our understanding of behavioural ecology. Changes in the expression of candidate genes can reveal their contribution to behavioural variation and/or phenotypic plasticity. Knowledge of gene function also enables experimental manipulation of behaviour in the lab and in the field. The candidate gene approach provides an accessible and useful tool for generating insights about animals that are not typically associated with genetic experimentation.