Heinz Giegerich investigates the way in which alternations in the sound patterns of words interact with the processes of word formation in the language. Drawing examples from English and German, he uncovers and spells out in detail the principles of "lexical morphology and phonology," a theory that has in recent years become increasingly influential in linguistics. He queries many of the assumptions previously made in it to produce a formally coherent theory that offers new accounts of some central phenomena in the phonology of English.