The Istaby Runestone, listed in the Rundata catalog as DR 359, is a runestone with an inscription in Proto-Norse which was raised in Istaby, Blekinge, Sweden, during the Vendel era.
The Istaby, Stentoften Runestone and Gummarp Runestone inscriptions can be identified with the same clan through the names that are mentioned on them. The names have alliterative first name element combined with a lycophoric second element that represent an aristocratic naming tradition common among chieftains. The Björketorp Runestone lacks names and is raised some tens of kilometers from the others. However, it is beyond doubt that the Björketorp runestone is connected to them, because in addition to the special runic forms, the same message is given on the Stentoften Runestone. Of these, on stylistics grounds, the Istaby runestone may be the oldest.
The name Hariwulfa is a combination of hari meaning "warrior" and wulafa "wolf," while the haþu of Haþuwulfz means "battle" and the heru of Heruwulfar, when combined in personal names, means "sword." The latter name also has a suffix indicating paternal decent, so the name Heruwulfar in full means "of the family of Sword-Wolf." A shortened form of the name Hariwulfa survived into the Viking Age and is attested in the inscription on the Hærulf Runestone. It has been suggested that the assignment of such lycophoric names is related to ritualistic practices and religious wolf-symbolism used in the initiation of young warriors.
The Istaby runestone is currently located at the Swedish Museum of National Antiquities in . The stone has a Danish Rundata catalog number as Blekinge was part of the historic Denmark.