|Abstract:||The focus of this paper is on metathesis, the process whereby in certain languages, under certain conditions, sounds appear to switch positions with one another. The paper takes as a starting point the view that a more comprehensive understanding of metathesis can be attained by investigating both formal and functional aspects of the process. To this end, the focus is, in part, on the potential influence on metathesis of factors external to phonology, including perception, production, cognition, and society. As a means of situating this discussion within a broader context, I begin by briefly laying out relevant assumptions concerning the interplay of external factors and phonology, in general. The focus then shifts to the characterization of metathesis within phonological theory. In particular, I present a sketch of a formal theory of metathesis within Optimality Theory. Conclusions and implications for phonological theory, and the interplay of functional factors and phonology are discussed.