This dissertation is an examination of Papago derivational morphology. Chapter One proposes a classification of lexical items based on the elements g and s in Papago. There is a category of lexical items which takes g, but not s (g-words), a category of lexical items which takes s, but not g (s-words), and a category of lexical items which take neither (0-element words). The classification, established on purely formal grounds, has clear semantic correlates. Further, given these three categories, the logical possibilities for derivational morphology are the following: g-word to g-word, g-word to s-word, g-word to 0-element word, 0-element word to 0-element word, 0-element word to g-word, 0-element word to s-word, and s-word to s-word, s-word to g-word, and s-word to 0-element word. Not all of these are instantiated; in particular, s-words are not subject to this simple derivational scheme. Chapters Two through Five present an analysis of a representative sample of derivational suffixes in Papago, exemplifying the first six logical possibilities. Chapter Six discusses the complications posed by s-words.