This fourth addition to the Old Assyrian Bibliography follows the structure of OAAS 1 [C. Michel, Old Assyrian Bibliography of Cu-neiform Texts, Bullae, Seals and the Results of the Excavations at Aššur, Kültepe/Kaniš, Acemhöyük, Alişar and Boğazköy, Leiden, 2003], OAB 1 [C. Michel, Old Assyrian Bibliography 1 (February 2003 - July 2006), AfO 51 (2005-2006), p. 436-449], OAB 2 [C. Michel, Old Assyrian Bibliography 2 (August 2006 - April 2009), AfO 52 (2011), p. 416-437] and OAB 3 [C. Michel, Old Assyrian Bibliography (May 2009 - March 2015), AfO 53 (2015), p. 525-559]. It contains corrections and additions to OAAS 1, OAB 1, OAB 2 and OAB 3: books and articles published between April 2015 and December 2019, titles published before and forgotten in the previous issues, reviews, new tablets discovered during the excavations or housed in private collections, line quotations of tablets preserved in the Museum of Anatolian Civilizations in Ankara and Kayseri, etc.