In his major work "Die reine Rechtslehre" (1934) Hans Kelsen intended to establish a legal science (Rechtswissenschaft) devoid of value judgements. The construction of a "basic norm" (Grundnorm) formed the basis for a purely scientific systematization of legal norms. Kelsen constructed the outlines for his legal doctrine in clear opposition to natural law theory. The latter was, in Kelsen's view, a metaphysical legal order, that continued to influence legal science, despite the apparent dominance of legal positivism in contemporary jurisprudence. Hence, it is unsurprising that Kelsen's work strongly emphasized the differences between "die reine Rechtslehre" and natural law theory. It does not follow, however, that Kelsen's legal theory differs from natural law theory in every respect. In fact, there are strong reasons to assume that a comparison of the two theories would in fact reveal some striking similarities. This would seem to be true, both in relation to the structure and the function of the two theories. This chapter offers an analysis of the concept of legal systematics in natural law theory and in Kelsen's "reine Rechtslehre". The point of departure is the concept of systematics in natural law theory.