This chapter starts with a simple demonstration of attention in action – in the form of a card trick. Considering attention as an evolved system then it is worth considering the potential survival benefits of being able to allocate attention to a region of space, either to search for objects or to be ready for when something does appear in that region. In ‘feature integration theory’ attention is conceptualised as a ‘cognitive glue’ that binds the features that make up a single object together. Different sensory features (colour, line-orientation, etc.) are coded by specialised independent sub-systems or ‘modules’, and each module forms a ‘feature map’ for the dimensions of the feature it encodes (plotting the locations of that feature). Evidence for top-down influences on attention has been provided by cueing studies. Posner’s original experiments measured the effects of providing participants with a visual cue which indicated the probability of a location where a visual target could appear.