Trilobite occurrences and biodiversity from Devonian sections of the Ardennes Massif are presented. Fluctuations in diversity reflect environmental changes and event-stratigraphic turnovers throughout the Devonian. Peak diversity is attained during the Eifelian (Middle Devonian) when the carbonate system is developed. Six trilobite associations have been delineated based on cluster analysis. Distribution of these associations is correlated with the deposition environments and age of the strata.