Summary Stanislaw Lubieniecki (1623-1675) was a Polish nobleman and adherent to the Unitarian religion. After his coreligionists were expelled from Poland and Lithuania in 1658, he settled in Hamburg and in the neighbouring town of Altona. When a comet appared in the sky in late 1664, Lubieniecki entered into correspondence with about forty astronomers, mathematicians and other scholars - Giovanni Battista Riccioli, Athanasius Kircher, Otto von Guericke, Erasmus Bartholin and Ismaël Boulliau, among others. Johannes Hevelius was one of the addressees of his letters, and their correspondence turned out to be long-lasting and abundant. In the years 1664-1673, they exchanged 92 letters (31 from Hevelius, 61 from Lubieniecki). This correspondence is the fourth most voluminous in the entire corpus of Hevelius's letters. Hevelius was a reputed astronomer, sometimes unwilling to share his observations and ideas, and Lubieniecki was an interested dilettante, striving to learn more about the comets of 1664 and 1665 and other astronomical phenomena as well as their significance. He wanted to collect as many accounts of contemporary and historical comets as possible, and he published them in his Theatrum cometicum. Even though at the same time Hevelius worked on his Cometographia, they both realized that their books touched upon different aspects of cometary studies: historical in the Theatrum cometicum and astronomical in Cometographia. This volume is a part of the edition of Johannes Hevelius's correspondence. The collection of letters, whose manuscripts are kept in the Library of the Paris Observatory, has not been published nor thoroughly studied yet. TABLE OF CONTENTS INTRODUCTION 1 : Stanislaw Lubieniecki and his Theatrum cometicum 1.1. The Life of Stanislaw Lubieniecki 1.2. Outline of Cometary Studies in Lubieniecki's Time 1.3. Theatrum cometicum 2 : The Hevelius-Lubieniecki Correspondence 2.1. The Number of Letters 2.2. Overview of the Correspondence 2.3. Hevelius's Input to Lubieniecki's Cometary Discussions 2.4. Overlap of Hevelius's and Lubieniecki's Networks 3 : Lubieniecki and the Heavens 3.1. Lubieniecki and the Theatrum cometicum in the Critical Literature 3.2. Lubieniecki and Astronomy 3.3. Lubieniecki and Astrology 3.4. Lubieniecki's Astronomical Correspondence 3.5. Letters in the Theatrum cometicum 4 : Editorial Principles CORRESPONDENCE APPENDICES Appendix 1. : Lubieniecki's Extract from Hevelius's Prodromus cometicus Appendix 2. : Lubieniecki's Extract from Hevelius's Descriptio cometae Appendix 3. : Lubieniecki's Opinion on the Meaning of Comets BIBLIOGRAPHY INDICES