To condemn the principles and doctrines of Protestantism and to clarify the doctrines of the Catholic Church on all disputed points. It is true that the emperor intended it to be a strictly general or truly ecumenical council, at which the Protestants should have a fair hearing. He secured, during the council's second period, 1551–1553, an invitation, twice given, to the Protestants to be present and the council issued a letter of safe conduct (thirteenth session) and offered them the right of discussion, but denied them a vote. Melanchthon and Johannes Brenz, with some other German Lutherans, actually started in 1552 on the journey to Trent. Brenz offered a confession and Melanchthon, who got no farther than Nuremberg, took with him the Confessio Saxonica. But the refusal to give the Protestants the vote and the consternation produced by the success of Maurice in his campaign against Charles V in 1552 effectually put an end to Protestant cooperation.

    To effect a reformation in discipline or administration. This object had been one of the causes calling forth the reformatory councils and had been lightly touched upon by the Fifth Council of the Lateran under Pope Julius II. The obvious corruption in the administration of the Church was one of the numerous causes of the Reformation. Twenty-five public sessions were held, but nearly half of them were spent in solemn formalities. The chief work was done in committees or congregations. The entire management was in the hands of the papal legate. The liberal elements lost out in the debates and voting. The council abolished some of the most notorious abuses and introduced or recommended disciplinary reforms affecting the sale of indulgences, the morals of convents, the education of the clergy, the non-residence of bishops (also bishops having plurality of benefices, which was fairly common), and the careless fulmination of censures, and forbade duelling. Although evangelical sentiments were uttered by some of the members in favour of the supreme authority of the Scriptures and justification by faith, no concession whatsoever was made to Protestantism.

    The Church is the ultimate interpreter of Scripture.[18] Also, the Bible and Church Tradition (the tradition that made up part of the Catholic faith) were equally and independently authoritative.

    The relationship of faith and works in salvation was defined, following controversy over Martin Luther's doctrine of "justification by faith alone".

    Other Catholic practices that drew the ire of reformers within the Church, such as indulgences, pilgrimages, the veneration of saints and relics, and the veneration of the Virgin Mary were strongly reaffirmed, though abuses of them were forbidden. Decrees concerning sacred music and religious art, though inexplicit, were subsequently amplified by theologians and writers to condemn many types of Renaissance and medieval styles and iconographies, impacting heavily on the development of these art forms.

The doctrinal decisions of the council are divided into decrees (decreta), which contain the positive statement of the conciliar dogmas, and into short canons (canones), which condemn the dissenting Protestant views with the concluding "anathema sit" ("let him be anathema").