The many aspects of Catholic activity during the sixteenth century make it difficult to present a systematic bibliography for that period. Interest in the Reformation era has considerably increased among Catholic scholars during the last decades. We must therefore proceed to a severe selection. Only studies that deal with the most significant topics will be included. No breakdown of the material can be completely satifactory. As the main point, however, is to give as clear a picture as possible, one must distinguish three broad periods: before, during and after the Council of Trent. Subdivisions of the subject matter in each period will necessarily overlap. But we will reduce this to a minimum.