Abstract This paper is a critical review of the principal problems in the taxonomy of the Chelicerata at higher levels. Of systems proposed, most are highly opinable and based on second-hand, uncontrolled information. A cladistic methodology has rarely been used. The only point generally accepted is the validity of most recent orders; the only progress made in the last fifty years appears to be the definitive solution of the problem of the position of the Xiphosura. Remarkable also is the lumping together of the two “classes” of the Merostomata and the Arachnida.