A plenary indulgence is removal of all of the temporal punishment due to sin. (Catechism 1471)
How Does one Obtain a Plenary Indulgence?
According to the Enchiridion of Indulgences 1968:
To acquire a plenary indulgence it is necessary to perform the work to which the indulgence is attached and to fulfill three conditions: sacramental confession, Eucharistic Communion and prayer for the intentions of the Supreme Pontiff. It is further required that all attachment to sin, even to venial sin, be absent.
The three conditions may be fulfilled several days before or after the performance of the prescribed work; nevertheless it is fitting that Communion be received and the prayers for the intentions of the Supreme Pontiff be said the same day the work is performed.
The condition of praying for the Supreme Pontiff's intentions is fully satisfied by reciting one Our Father and one Hail Mary; nevertheless the individual faithful are free to recite any other prayer according to their own piety and devotion toward the Supreme Pontiff.
If this disposition is in any way less than complete, or if the Prescribed three conditions are not fulfilled, the indulgence will only be partial, except for the provisions contained in No. 11 for those who are "impeded."
Plenary Indulgence Available on All Souls Day:
As today is November 2nd, I thought I would include this special plenary indulgence only available on November 2nd:
According to the Enchiridion of Indulgences, a plenary indulgence applicable only to the dead can be acquired in all churches and public oratories -- and in semipublic oratories by those who have the right to use them --on November 2.
In visiting the church or oratory, it is required, according to Norm 16 of the same Apostolic Constitution, that "one Our Father and the Creed be recited."
Indulgences Available to those who use with Devotion a Blessed Object:
The faithful who use with devotion an object, piety (crucifix, cross, rosary, scapular or medal) properly blessed by any priest, can acquire a partial indulgence.
It is desirable to obtain a blessing of the object from a bishop or the Pope.
If this object of piety is blessed by the Supreme Pontiff or any bishop, the faithful who use it devoutly can also acquire a plenary indulgence on the feast of the holy Apostles Peter and Paul, provided they also make a profession of faith using any legitimate formula.(Enchiridion of Indulgences 1968)