For the first time, a scholarly theological library of the early modern period has been reconstructed in this work. The ‹Bibliotheca Gerhardina‹, established by Johann Gerhard and his son Johann Ernst, contains more than 6,000 bibliographical units and is one of the largest private book collections of the 17th century. The first volume of the set is an edition of the complete handwritten catalogue by J. E. Gerhards. In the second volume, there are bibliographic records for all publications concerned in accordance with modern standards along with their present location. All of the publications in the ‹Bibliotheca Gerhardina‹ have been taken into account, including those which are not listed in the catalogue. Both volumes are linked by an easily understandable numbering system. The indexes of authors/editors, printers, publishers, place of printing and location of publishing company, make this work user-friendly.