My research explores the typology of morphological complexity, with a particular focus on processes of variation and change. If language typology is to be more than a catalogue of curiosities, it should be a typology of trajectories of change. By understanding processes of language change, we can understand how typological diversity has arisen, and how it is constrained. The catalogue of diverse linguistic structures thereby becomes a window into the cognitive and social forces that shape language evolution, and typological description becomes the proper source of linguistic theory. Morphology is a particularly fruitful sub-discipline for this typological endeavour, as languages show extreme diversity in the morphological structure of words. My research aims to discover how diverse word structures evolve, how they are cognitively processed and how they are deployed in social interaction.