Palaeozoic, Mesozoic and Cenozoic guide fossils, chronologically important within the areas of western and northern Canada and Alaska, are described and illustrated. Most generalizations can also be applied to eastern Canada and the United States. Emphasis is upon fossil groups rather than genera and species, and particularly upon those which a geologist may identify in the field with minimum chances for error. The groups stressed are fusulinid foraminifera, stromatoporoids, graptolites, corals, brachiopods, pelecypods, cephalopods and trilobites. Finer divisions are established for most of these groups, alone with trends, genera and species, which can safely be used in correlation.