The arthropod subphylum Chelicerata encompasses ~ 110,000 described living species. Here we review the present state of knowledge on chelicerate phylog- eny, thereby including morphological, paleontological and molecular evidence. We must conclude that chelicerate relationships are largely unresolved. The minimal con- sensus tree supported by various methods is (Pycnogonida, (Xiphosura, (Scorpiones, ((Amblypygi, (Thelyphonida, Schizomida)), Araneae)))). In addition, the Acari – com- bining Acariformes and Parasitiformes – are probably a valid taxon. The positions of Opiliones, Palpigradi, Pseudoscorpiones, Ricinulei, and Solifugae are, however, essentially unresolved. Even a novel large multi-gene data set derived from expressed sequence tags from various chelicerate taxa did not help improving the tree. The lack of phylogenetic signal may be explained by rapid adaptive radiation associated with the terrestrialization of the arachnids.