This week, Archbishop Ireland Memorial Library has put up a display about the Index of Prohibited Books, published for centuries by the Catholic Church. Beginning in 1557 and issued regularly until 1948 (officially abolished in 1966), the purpose of The Index was to protect Catholics from books deemed dangerous to their faith and morals.
Displayed at Ireland Library are different editions of The Index and some interesting books that were on the list. Among the notables writers appearing on The Index were Galileo, Erasmus, Gibbon, Kant, Voltaire, Flaubert, Swedenborg, Descartes, Locke, Sartre, Balzac.
In the aftermath of Vatican II, the Church’s position had evolved and The Index was eventually discontinued. Canon Law 212 (section 3) now obtains:

They [the faithful] have the right, indeed at times the duty … to manifest to the sacred Pastors their views on matters which concern the good of the Church. They have the right also to make their views known to others of Christ’s faithful, but in doing so they must always respect the integrity of faith and morals, show due reverence to the Pastors and take into account both the common good and the dignity of individuals.

For a list of books and authors who, at one time or another, were on The Index see Index Librorvm Prohibitorvm—1948. Also, The New Catholic Encyclopedia has an in depth article.
Some trivia:
No American novelist (and very few American non fiction works) was ever on The Index.
Jean Steinmann’s La Vie de Jesus had the distinction of being the last work ever prohibited (1959). This book is on display at Ireland Library, this week.