From the Manual on Indulgences, published 2006 by the USCCB, being a translation of the Enchiridion Indulgentiarum quarto editur.

N1. An indulgence is a remission before God of the temporal punishment for sins, whose guilt is forgiven, which a properly disposed member of the Christian faithful obtains under certain and clearly defined conditions through the intervention of the Church, which, as the minister of Redemption, dispenses and applies authoritatively the treasury of the expiatory works of Christ and the saints.

N2. An indulgence is partial or plenary according to whether it removes either part or all of the temporal punishment due sin.

N3. The faithful can obtain partial or plenary indulgences for themselves, or they can apply them to the dead by way of suffrage.

N4. The faithful who perform with at least inward contrition an action to which a partial indulgence is attached obtain, in addition to the remission of temporal punishment acquired by the action itself, an equal remission of punishment through the intervention of the Church.

N13. If a liturgical celebration or its external solemnity is lawfully transferred, it is understood that an indulgence attached to that liturgical celebration is likewise transferred to the same day.

N14. If a visit to a Church or an oratory is required to obtain an indulgence attached to a particular day, this may be accomplished from noon of the preceding day until midnight of the particular day.

N15. The faithful can acquire an indulgence if they use devoutly one of the following properly blessed pious objects, namely: a crucifix or cross, rosary, scapular, or medal.

N16. §1. Indulgences attached to visiting a church or oratory do not cease if the church is totally destroyed and then rebuilt within fifty years in the same or almost the same place and under the same title.
§ 2. An indulgence attached to the use of an article of devotion ceases only if the article is destroyed or sold.

N17 §1. In order to be capable of gaining indulgences one must be baptized, not excommunicated, and in the state of grace at least at the completion of the prescribed works.
§2. To gain an indulgence, one must have at least the general intention of doing so and must carry out the enjoined works at the stated time and in due fashion, according to the sense of the grant.

N18. §1. A plenary indulgence can be acquired only once in the course of a day; a partial indulgence can be acquired multiple times.
§2. The faithful however can obtain the plenary indulgence at the hour of death, even if they have already gained one on the same day.

N19. The work prescribed for acquiring a plenary indulgence connected with a church or oratory consists of a devout visit during which an Our Father and the Creed are recited, unless other directives have been laid down.

N20. §1. To gain a plenary indulgence, in addition to excluding all attachment to sin, even venial sin, it is necessary to perform the indulgenced work and fulfill the following three conditions:
sacramental confession, Eucharistic Communion, and prayer for the intention of the Sovereign Pontiff.
§2. A single sacramental confession suffices for gaining several plenary indulgences; but Holy Communion must be received and prayer for the intention of the Holy Father must be recited for the gaining of each plenary indulgence.
§ 3. The three conditions may be fulfilled several days before or after the performance of the prescribed work; it is, however, fitting that Communion be received and the prayer for the intention of the Holy Father be said on the same day the work is performed.
§4. If the full disposition is lacking, or if the work and the three prescribed conditions are not fulfilled, saving the provisions given in Norm 24 and in Norm 25 regarding those who are “impeded,” the indulgence will only be partial.
§5. The condition of praying for the intention of the Holy Father is fully satisfied by reciting one Our Father and one Hail Mary; nevertheless, one has the option of reciting any other prayer according to individual piety and devotion, if recited for this intention.

N21. §1. Unless otherwise stated, an indulgence cannot be gained by a work already imposed by law or precept.
§ 2. One, however, who performs a work which has been imposed as a sacramental penance and which happens to be one enriched with an indulgence, can at the same time both satisfy the penance and gain the indulgence.
§ 3. Similarly, members of institutes of consecrated life and societies of the apostolic life can obtain the indulgences attached to prayers and pious works already obligatory by reason of their rules and constitutions or by precept.

N22. An indulgence attached to a prayer can be acquired by reciting the prayer in any language, provided that the translation is approved by the competent ecclesiastical authority.

N23. To gain an indulgence it is sufficient to recite the prayer alternately with a companion or to follow it mentally while it is being recited by another.

N24. Confessors can commute either the prescribed work or the conditions in favor of those for whom these are impossible because of a legitimate impediment.

N25. Hierarchs or local ordinaries can grant permission to the faithful over whom they exercise legitimate authority and who live in places where it is impossible or at least very difficult to go to confession or Communion to gain a plenary indulgence without confession and Communion, provided they have contrition for their sins and have the intention of receiving these Sacraments as soon as possible.

N26. Both the deaf and the mute can gain indulgences attached to public prayers if, together with the other faithful praying in the same place, they devoutly raise their mind and affections to God; regarding private prayers it is sufficient for them to recite the prayers mentally or express them with signs, or simply to read them without pronouncing the words.