This article begins with a sketchy historical introduction to the topic, which will help bring into focus some of the pressing issues for philosophy in the twenty-first century. ‘Intentionality’ as it is typically used in analytic philosophy, meaning, roughly representationor ‘aboutness’, derives from the work of Franz Brentano. For Brentano mental states are essentially related to certain kinds of objects or contents that have ‘intentional inexistence’ within the states. These came to be called ‘intentional objects’. Brentano was particularly concerned with the problem of how we can represent things that don't exist outside of the mind, such as unicorns.