In this thesis, some of the methods by which animals use their sensory systems to interact with their environment have been extensively studied. How gene duplications have played an important role in sensory evolution by duplication followed by functional shifts resulting in neofunctionalisation has been analysed. This extensive neofunctionalisation allows for an expansion in the number of environmental signals the animal can detect. In the following chapters, some of the ways gene duplication has effected sensory perception have been shown in detail, in particular by the expansion and specialisation of sensory receptor repertoires. Chapter two describes an extensive study performed on the duplication and neofunctionalisation of opsins in animals as a result of environmental signals, leading to the evolution of colour vision. This study of vision is expanded upon in chapter three by looking at how the duplication of an entire visual pathway has led to the emergence of a new cell type and visual function in the rod and cone cells of vertebrates. Finally, in chapter four, large-scale analyses were performed of some massively expanded gene families used for olfactory and gustatory discrimination, showing the effects of extreme cases of gene duplication on animal sensory perception.