1. Regional distribution of Carabid beetles in Belgium (1) The study of regional distribution of Carabid beetles is preceded by a detailed analysis of potential ecological factors such as, altitude, climate, geology, pedology and lithology. The analysis sets up a mapping of geographically homogeneous areas. Ordination methods reveal a strong gradient in the set of potential ecological factors taken to account. This gradient is strongly correlated with altitude. Although maximum altitude in Belgium is 700 m, this factor explains most of the geographical structure, because all the other variables are correlated with it. Yet, edaphic conditions isolate the Belgian Lorraine from the other Belgian regions. In spite of the existence of the altitudinal gradient, several homogeneous regions separated from one another by stable frontiers are evident. These frontiers correspond to the maximal discontinuity zones of the local distribution of all potential ecological variables examined. The established frontiers are not artefacts produced on a continuous gradient but are real natural geographic boundaries. (2) Although the biogeographic structure is not as clear as the geographic structure, analysis of the distribution of Carabid beetles in Belgium allows us to define five biogeographic regions: the Coast, the sandy-loamy Flanders, the chalky regions (Condroz-Fagne-FamenneCalestienne and Belgian Lorraine) and the Ardennes plateau. A classification of the species in eight clusters, corresponding to different types of distribution, is established. Beside species groupes with geographical affinities explained by their ecological requirements, a cluster of rare species and one of species found on a large scale were evident. The role of the different potential factors of distribution has been evaluated. 15 to 20% of the total variance of the distribution data is directly explained by the factors of distribution. Among these, the principle factor is the topographic gradient. The climatic and edaphic factors seem to occur with the ...