The introduction, addressed to “Christian readers,” is written over the signatures of the rector and the members of the general faculty of the university. The writers point out that the lists of prohibited books include not only such as are to be classed as heretical or as very suspicious, but also others which, under the cover of religious instruction, are likely to mislead the unlearned or to convey erroneous views concerning the pope, the ceremonials of the Church, confession, mass, and the saints. Of the chief heretics, all the writings are prohibited, the names being in the main those that appear in the catalogue of 1540. The list includes Brunfels, Brenz, Bucer, Bullinger, Corvinus, Calvin, Petrus Martyr, Urbanus Regius, and Musculus. The names of Luther and Melanchthon are not included. The suggestion is made to students whose work would be hampered through the want of certain scholarly treatises, important in themselves and marred possibly only through a small proportion of heretical error, and in the case of texts from the Latin, Greek, Hebrew, or Chaldean, the annotations to which may contain error, that permission can be secured, by properly accredited applicants, from commissioners to be appointed for the purpose, for a restricted use of such volumes; or the commissioners will, at their discretion, eliminate from the volumes the heretical or dangerous portions, thus rendering them available for use in the class-room. This Louvain Index of 1550 was, in 1551, reprinted in Spain under the direction of Valdes, Inquisitor-General. Its lists (in the Latin text) were included in the Valdes Index of 1559, and in a number of other of the Indexes produced in Spain. The Latin lists were also utilised in the first of the Venetian Indexes and from this the titles were transferred to the Roman Index of 1559. The work of the theologians of Louvain was in fact accepted as the foundation or general model for the whole series of Indexes which were produced prior to the Council of Trent, and was indeed, through the Index of Paul IV, utilised by the compilers of the Tridentine Index of 1564. The Roman compilers, in including in their schedules the titles from the Louvain volume, transferred to Class I (comprising authors of acknowledged heresy, all of whose works were condemned) the names of a number of writers of whose productions the Louvain doctors had found but a few examples deserving of condemnation. These general heretics of Class I belong, with but one or two exceptions, to Germany and the Low Countries. From the heretical writers of France are selected Dolet and Marot, and from Italy, Ochinus and Curio.