Vishtaspa (Avestan: 𐬬𐬌𐬱𐬙𐬁𐬯𐬞𐬀 Vištāspa; Old Persian: 𐎻𐏁𐎫𐎠𐎿𐎱 Vištāspa; Persian: گشتاسپ Guštāsp; Ancient Greek: Ὑστάσπης Hustáspēs) is the Avestan-language name of a figure appearing in Zoroastrian scripture and tradition, portrayed as an early follower of Zoroaster, and his patron, and instrumental in the diffusion of the prophet's message. Although Vishtaspa is not epigraphically attested, he is – like Zoroaster – traditionally assumed to have been a historical figure, although obscured by accretions from legend and myth.

In Zoroastrian tradition, which builds on allusions found in the Avesta, Vishtaspa is a righteous king who helped propagate and defend the faith. In the non-Zoroastrian Sistan cycle texts, Vishtaspa is a loathsome ruler of the Kayanian dynasty who intentionally sends his eldest son to a certain death. In Greco-Roman literature, Zoroaster's patron was the pseudo-anonymous author of a set of prophecies written under his name.

Vishtaspa is referred to in the Gathas, the oldest texts of Zoroastrianism which were considered to have been composed by Zoroaster himself. In these hymns, the poet speaks of Vishtaspa as his ally (Yasna 46. 14), follower of the path of Vohu Manah (Y. 51. 16), and committed to spreading the prophet's message (Y. 51. 16, 46. 15, 53. 2). In Yasna 28. 1–28. 7, Zoroaster appeals to Mazda for several boons, including the power to vanquish their foes for Vishtaspa and himself. Considered collectively, the Gathas celebrate Vishtaspa as the "patron of Zoroaster and the establisher of the first Zoroastrian community. "

The Gathic allusions recur in the Yashts of the Younger Avesta. The appeal to Mazda for a boon reappears in Yasht 5 (Yt. 5.98), where the boon is asked for the Haugvan and Naotara families, and in which Vishtaspa is said to be a member of the latter. Later in the same hymn, Zoroaster is described as appealing to Mazda to "bring Vishtaspa, son of Aurvataspa, to think according to Daena (Religion), to speak according to the Religion, to act according to the Religion." (Yt. 5. 104–105). In Yasht 9. 25–26, the last part of which is an adaptation of the Gathic Yasna 49. 7, the prophet makes the same appeal with regard to Hutaosa, wife of Vishtaspa.

In Yasht 9.30, Vishtaspa himself appeals for the ability to drive off the attacks of the daeva-worshipping Arejataspa and other members of drujvant Hyaona family. Similarly in Yasht 5. 109, Vishtaspa pleads for strength that he may "crush Tathryavant of the bad religion, the daeva-worshipper Peshana, and the wicked Arejataspa." Elsewhere (Yt. 5. 112–113), Vishtaspa also pleads for strength on behalf of Zairivairi (Pahl. Zarēr), who in later tradition is said to be Vishtaspa's younger brother. The allusions to conflicts (perhaps battles, see below) are again obliquely referred to in Yasht 13 (Yt. 13.99–13.100), in which the fravashis of Zoroaster and Vishtaspa are described as victorious combatants for Asha, and the rescuers and furtherers of the religion. This description is repeated in Yasht 19 (Yt. 19.84–19.87), where Zoroaster, Vishtaspa and Vishtaspa's ancestors are additionally said to possess khvarenah. While the chief hero of the conflicts is said to be Vishtaspa's son, Spentodhata, (Yt. 13. 103) in Yasht 13. 100, Vishtaspa is proclaimed to have set his adopted faith "in the place of honor" amongst peoples.

Passages in the Frawardin Yasht (Yt. 13.99–13.103) and elsewhere have enabled commentators to infer family connections between Vishtaspa and several other figures named in the Avesta. The summaries of several lost Avestan texts (Wishtasp-sast nask, Spand nask, Chihrdad nask, and Warshtmansr nask), as reported in the Denkard (respectively 8. 11, 8. 13, 8. 14, and 9. 33. 5), suggest that there once existed a detailed "history" of Vishtaspa and his ancestors in scripture. The Yasht 13 mentions Zairiuuairi, Piší šiiaoθna (Vishtaspa's eschatological son Pišišōtan), Spəṇtōδāta (Spandyād), Bastauuairi (Bastwar), Kauuarazman, Frašaoštra and Jāmāspa (the Huuōguua brothers in the Gathas), all of whom are featured in the Pahlavi narrative about the war between Vishtaspa and Arzāsp (Arjāsp, king of the Xiiaonas). In Yasht 9.31, Vishtaspa prays to Druuāspā that he may successfully fight and kill various opponents and, apparently, turn Humaiiā and Varəδakanā away from the lands of the Xiiaonas.

In Yasna 12, the Zarathustra, Vishtaspa, Frašaoštra and Jāmāspa, and the three Saošiiaṇts, Zarathustra's eschatological sons, and in Yasna 23.2 and 26.5, the fravashi of Gaiia Marətān, Zarathustra, Vishtaspa, and Isaṯ.vāstra (another of Zarathustra's eschatological sons) are listed as the principal fighters for Asha.

The meaning of Vishtaspa's name is uncertain. Interpretations include "'he whose horses have (or horse has) come in ready (for riding, etc.)'"; "'he who has trained horses'"; and "'whose horses are released (for the race)'". It agrees with the description from Yasht 5.132 in which was a prototypical winner of the chariot race.