This book is an introduction to a general study of legal systems, that is, to the study of the systematic nature of law, and the examination of the presuppositions and implications underlying the fact that every law necessarily belongs to a legal system (the English, or German, or Roman, or Canon Law, or some other legal system). A comprehensive investigation may result in what could be called a theory of legal system. Such a theory is general in that it claims to be true of all legal systems. If it is successful it elucidates the concept of a legal system, and forms a part of general analytic jurisprudence. The approach to the subject adopted here is in part historical, and starts from a critical examination of previous theories. The constructive part of the work is analytical in character, and the authors examined in the historical part all belong to the analytic school of jurisprudence.