The nunciature in the city of Graz, the residence of the Inner Austrian line of the Habsburgs, was founded in 1580 and existed through 1622. Apart from the emperial nunciature it was the only diplomatic representation of the Holy See in the Habsburg hereditary lands in the early modern period. Direct contact between the Inner Austrian Habsburgs and the curia was maintained by the weekly reports of the nuncio to the papal secretariat of state and the instructions and replies thereto. This contact was at times intensified by the nuncio himself. This was especially the case during the unusually long term of office (1592-1607) of Girolamo Portia, who had a confidential relationship to the archducal family in Graz. The critical edition comprising the entire, mostly Italian-language correspondence of the Graz nunciature reflects the main political, economic, confessional and social problems and the transformation of cultural patterns at the local, regional and supra-regional levels. These events were formative for the young sovereign, Archduke Ferdinand, and also influenced his later reign as Emperor Ferdinand II. The fifth volume of the edition presented here encompasses the correspondence between the nuncio Portia and the secretariat of state of Pope Clemens VIII in the years 1599-1602. It gives insight into the re-Catholicization and inner clerical reform in Inner Austria, the Ottoman threat and the problem of financing the defense of the borders, the conflict between Inner Austria and the Republic of Venice due to the Uscocs, as well as aspects of daily life.