'''''Quo Primum''''' sont les deux premiers mots d'une bulle promulguée le 14 juillet 1570 par le pape Pie V. Ce texte a pour objet la publication d'un missel de référence dans l'Église latine. Le pape, en publiant la première édition typique du missel romain, rend celui-ci valide dans tout l'occident chrétien.

== Les origines de la messe romaine ==

== Le concile de Trente et la liturgie ==

== La bulle ==
Par la bulle ''Quo Primum'', le pape rend obligatoire l'utilisation de ce texte dans toute l'Église latine, en faisant exception uniquement pour les endroits ou un autre rite a été célébré pendant plus de deux cents ans. C'est ainsi que, entre autres, le rite ambrosien et le rite mozarabe et les rites de plusieurs instituts religieux ont pu continuer légalement leurs existence.

« Saint Pie V avait conçu l'édition du Missel romain comme un instrument d’unité catholique. En conformité avec les prescriptions du Concile de Trente, le Missel romain de saint Pie V devait empêcher que pût s'introduire dans le culte divin aucune des subtiles erreurs dont la foi était menacée par la Réforme protestante »<ref>[http://www.salve-regina.com/Liturgie/Bref_examen.htm « Bref examen critique des cardinaux Ottavianni et Bacci » §8 sur le site ''Salve Regina'']</ref>.
=== Le texte de la bulle ===
[http://www.salve-regina.com/Magistere/Bulle_Quo_primum_tempore.htm ''Quo primum tempore'' sur le site ''Salve Regina'']

'''''Quo Primum''''' (''from the first'') is the name of an Mass liturgy of at least two hundred years' standing.

The declared reason for this measure was: "It is most becoming that there be in the Church ... only one rite for the celebration of Mass."  However, he did make the exception mentioned, which permitted the survival, within limited areas or in celebrations by members of certain religious orders, of Ambrosian and Lyon and certain Catholic Order Rites. Some of these dioceses and religious orders have since decided to adopt the Roman Rite. Others preferred not to avail themselves of the exemption to which they were entitled and instead to adopt the Roman Missal immediately.

Thus, although the bull ''Quo primum'' contained expressions such as "Let all everywhere adopt and observe what has been handed down by the Holy Roman Church, the Mother and Teacher of the other Churches, and let Masses not be sung or read according to any other formula than that of this Missal published by Us. This ordinance applies henceforth, now, and forever, throughout all the provinces of the Christian world", exceptions were allowed from the start.

In the bull Pope Pius V declared: "By this present Constitution, which will be valid henceforth, now, and forever, We order and enjoin that nothing must be added to Our recently published Missal, nothing omitted from it, nor anything whatsoever be changed within it." And he concluded: "No one whosoever is permitted to alter this notice of Our permission, statute, ordinance, command, precept, grant, indult, declaration, will, decree, and prohibition. Should anyone dare to contravene it, let him know that he will incur the wrath of Almighty God and of the Blessed Apostles Peter and Paul."