This book breaks new ground by developing a formal computational theory of writing systems. It offers specific proposals about the linguistic objects that are represented by orthographic elements; what levels of linguistic representation are involved and how they may differ across writing systems; and what formal constraints hold of the mapping relation between linguistic and orthographic elements. Based on the insights gained, Sproat posits a new taxonomy of writing systems. The treatment of theoretical linguistic issues and their computational implementation is complemented with discussion of empirical psycholinguistic work on reading and its relevance for the computational model developed here. Throughout, the model is illustrated with a number of detailed case studies of writing systems around the world. This innovative book will be of interest to students and researchers in a variety of fields, including theoretical and computational linguistics, the psycholinguistics of reading and writing, and speech technology. "...this is easily the most original piece of writing in linguistics that I have read in the last ten years." Gerald Penn, Written Language & Literacy