The Middle Cambrian of Bohemia contains a widespread fauna which can be traced from eastern Newfoundland, through central Britain, Scandinavia and the Montagne Noire in France and further east. Whereas the upper Cambrian (Furongian) in Bohemia consists of volcanics and alluvial sediments, in the Scandinavian (Baltica) and Avalonian successions, dysoxic facies prevail, dominated by the olenid trilobites. The Furongian of southern Sweden forms a superb natural laboratory for studying processes and patterns of evolution in the olenids. The rapid turnover of species and superb preservation of the fossils allows evolutionary changes to be assessed stratophenetically, and at the microevolutionary scale. Also, the dynamics of the evolving faunas can be assessed and their relations with environmental fluctuations established by bed-by-bed collecting and analysis. Moreover since all trilobite growth stages often occur along with the adults, it is possible to establish the complete or partial ontogeny of many species, and to explore the relationhips between ontogeny and phylogeny. Information gained from various lines of evidence from the faunas can be used, along with geochemical approaches to build up a coherent picture of an extinct environment and its inhabitants; this paper summarises old and new explorations in this field.