The fourth volume of the series Sylloge Nummorum Sasanidarum, Paris-Berlin-Wien, covers the period of Khusro I (531-579). His long reign is generally considered the high point of Sasanian history. So far, numismatic research has only covered his coinage in overviews, but no detailed treatment has been compiled. Similarly, the number of coins properly published did not do justice to the importance of Khusro I's coinage. For the first time, a detailed numismatic analysis based on a representative collection of material can be presented. While the numismatic documentation is still far from complete, some developments now become visible for the first time. One focus is on the mint abbreviations, because analysis of these gives access to important new information for Sasanian administrative and regional history. The observation of numismatic parameters is of particular importance in this respect, and while style no longer offers relevant clues, some other topics, such as the patterns of minting, do; as a result, the important and productive mint signature WH can be firmly located in the region Khuzistan. The value of Sasanian coinage for the reconstruction of political history is also evaluated. One chapter is dedicated to material analysis. The catalogue covers about 880 coins from the collections in Paris, Berlin, and Vienna, as well as about 1200 additional coins. This is the most substantial documentation of the coinage of Khusro I compiled so far. The typology, legends and additional marks are documented and discussed in detail, with the text and catalogue divided into two separate volumes.