 He owes his worldwide reputation to his "Institutiones Juris Canonici", the text of which is reproduced in most editions of the "Corpus Juris Canonici".Following the example of the Byzantine Emperor Justinian, who had entrusted to three professors the task of drawing up an elementary work on Roman law entitled the "Institutiones", intended for use in the schools, Lancelotti conceived the plan of a like work on the Catholic Church's canon law.Pope Paul IV charged him officially with the execution of his plan, and for this purpose he went to Rome in 1557.