Detailed analysis of trilobite assemblages at the Cambrian–Tremadoc transition reveals the presence of four, possibly five, biogeographic provinces: Baltic, North China, Southeast China, North American, and possibly Siberian. One or more discrete biofacies characterize the transition in each province. When plotted palaeogeographically these appear to be largely temperature controlled. Interdigitation of provincialized trilobite biofacies is recognized by the representation of dominant types of trilobite, olenaceans, ceratopygaceans, remopleuridaceans, dikelocephalaceans and leio-stegiaceans in particular, on key boundary sections. These sections, at Nochixtlán, Mexico; Batyrbay, southern Kazakhstan; Broken Skull River, District of Mackenzie, Canada; and Jiangshan–Chang-shan, western Zhejiang, China, permit the correlation of biogeographic provinces globally. As a result of the application of trilobite biostratigraphy relatively few problems prevent the maintenance of a Cambrian–Ordovician Boundary stratotype section in its traditional Baltic biogeographic setting.