A major change took place in trilobite faunas during Late Cambrian and Early Ordovician time, that is, during the Tremadoc Epoch. The majority of preexisting families died out shortly before or during this epoch. They were replaced by several short-lived, new groups and the earliest members of other families which dominated succeeding Ordovician trilobite faunas. The dissimilarities between samples of Tremadoc trilobite faunas from 18 areas in the world were analyzed by a nonmetric multidimensional scaling technique. Groupings obtained by such analyses reveal faunal provinces of the Ordovician, and for the early part of the period 4 provinces were recognized. The analyses of Tremadoc faunas should reveal whether or not changes in provinces occurred during this epoch. The assumption that a faunal province originally extended over the shallow seas surrounding a single continental mass is used, with palaeomagnetic data, to propose a model for Tremadoc paleogeography.