The author deals with the legal theoretical approach that has been labelled “legal institutionalism.” An old and a new version of this approach are singled out: The old one is identified with the theory defended by the Italian public lawyer Santi Romano in the first half of this century; the second one is seen in the recent work by Ota Weinberger and Neil MacCormick. After a short presentation of Romano's work, his ideas and the development proposed by MacCormick and Weinberger (...) are compared. Similarities and differences between the two versions of institutional theory are worked out. A coda hints at an ambiguity in the definition of institution proposed by the “new” institutionalism. (shrink)