The authors present a short summary of the actual knowledge on the Paleozoic of the western Alps. Special attention is directed to the crystalline external massivs (Aiguilles-Rouges, Mont-Blanc, etc.) and the Pennine nappes, where it is possible to recognize several units of distinct ages, probably from late Precambrian to late Paleozoic. The similarities between some metamorphosed series from different tectonic units are put in evidence and the possible origin and age of these series (Schistes de Casanna, série des Aiguilles- Rouges, etc.) are discussed, particularly in the light of geochronometric datations.