This prayer was composed by Pope Leo XIII following a vision he had after celebrating the Mass. In this vision, the Pope heard a conversation between Our Lord and satan. The vision affected him so much that upon recovering, he immediately composed this prayer. 

This short version was said after every Mass from that day forward until Vatican II. The long version is in english.

It has been recommended that we say this prayer at least once a week, and if you are facing tribulation, once a day.

 

Sancte Michael Archangele, defende nos in proelio, contra nequitiam et insidias diaboli esto praesidium. Imperet illi Deus, supplices deprecamur: tuque, Princeps militiae coelestis, Satanam aliosque spiritus malignos, qui ad perditionem animarum pervagantur in mundo, divina virtute, in infernum detrude. Amen.