The Liber Septimus (Latin for "Seventh book") may refer to one of three Catholic canon law collections of quite different value from a legal standpoint which are known by this title.
[1] It was officially promulgated by Clement V in a consistory held at Monteaux, near Carpentras (southern France) on 21 March 1314, and sent to the University of Orléans and the Sorbonne in Paris.
It owes the name of "Liber Septimus" to Cardinal Pinelli, prefect (president) of the special congregation appointed by Sixtus V to draw up a new ecclesiastical code, who applied this title to it in his manuscript notes; Prospero Fagnani and Benedict XIV imitated him in this, and it has retained the name.
[1] It was to supply the defect of an official codification of the canon law from the date of the publication of the Constitutiones Clementinæ (1317), that Gregory XIII appointed about the year 1580 a body of cardinals to undertake the work.
A new revision undertaken in 1607-08 had a similar fate, the reigning pope Paul V declining to approve the Liber Septimus as the obligatory legal code of the Church.