Spāhbad (also spelled spahbod) is a Middle Persian title meaning "army chief" or commander used chiefly in the Sasanian Empire. Originally there was a single spāhbad, called the Ērān-spāhbed, who functioned as the generalissimo of the Sasanian army. From the time of Khosrow I (r. 531–579) on, the office was split in four, with a spāhbad for each of the cardinal directions. After the Muslim conquest of Persia, the spāhbed of the East managed to retain his authority over the inaccessible mountainous region of Tabaristan on the southern shore of the Caspian Sea, where the title, often in its Islamic form ispahbedh (Persian: اسپهبذ; in Arabic: اصبهبذ ʾiṣbahbaḏ), survived as a regnal title until the Mongol conquests of the 13th century. An equivalent title of Persian origin, ispahsālār or sipahsālār, gained great currency across the Muslim world in the 10th–15th centuries.

The title was also adopted by the Armenians (Armenian: սպարապետ, [a]sparapet) and the Georgians (Georgian: სპასპეტი, spaspeti), as well as Khotan (spāta) and the Sogdians (spʾdpt) in Central Asia. It is also attested in Greek sources as aspabedēs (ἀσπαβέδης). The title was revived in the 20th century by the Pahlavi dynasty, in the Modern Persian form sepahbod (سپهبد), equivalent to a three-star Lieutenant General, ranking below arteshbod (full General).

The title is attested^{[failed verification]} in the Achaemenid Empire in its Old Persian form, spādapati (from *spāda- "army" and *pati- "chief"), signifying the army's commander-in-chief. The title continued in use under the Arsacid Parthian Empire, where it seems to have been a hereditary position in one of the seven great houses of the Parthian nobility.

The Sasanian Empire, which succeeded the Arsacids, retained the title, which is attested in a series of inscriptions from the 3rd century, recorded in Middle Persian (Inscriptional Pahlavi script) as 𐭮𐭯𐭠𐭧𐭯𐭲𐭩 spʾhpty and 𐭮𐭯𐭠𐭧𐭯𐭲 spʾhpt (read as spāhbed) and in Parthian (Inscriptional Parthian script) as 𐭀𐭎𐭐𐭀𐭃𐭐𐭕𐭉‎ ʾspʾdpty and 𐭎𐭐𐭃𐭐𐭕𐭉‎ spdpty (read as (a)spāẟbed).

Until the early 6th century, there was a single holder of the title, the Ērān-spāhbed, who according to the list of precedence provided by the 9th-century Muslim historian Ya'qubi occupied the fifth position in the court hierarchy. Two spahbads, both named Raxš, are recorded in Shapur-KZ and Paikuli inscriptions.

The Byzantine and Syriac sources record a number of senior officers who might be holders of the rank in the early 6th century. Thus during the Anastasian War of 502–506, a certain Boes (Bōē), who negotiated with the Byzantine magister officiorum Celer and died in 505, is named in the Syriac sources as an 'astable' (also spelled astabed, astabad, astabadh). His unnamed successor in the negotiations also bore this title. Some modern scholars have interpreted astabed as a new office corresponding to the Byzantine magister officiorum, supposedly instituted by Kavadh I shortly before 503 for the purpose of weakening the authority of the wuzurg framadar. But it is likely that this Syriac word is simply a corrupted form of spāhbed (which is normally recorded as aspabid in Syriac), or possibly asp(a)bed ("chief of the cavalry"), since the Greek sources give the name of the second man as Aspebedes (Latin: Aspebedus), Aspevedes, or Aspetios (Latin: Aspetius). Again, during the Iberian War (526–532), a man named Aspebedes (i.e. Bawi), according to the historian Procopius a maternal uncle of Khosrow I (r. 531–579), appears. In 527 he took part in negotiations with Byzantine envoys, and in 531 he led an invasion of Mesopotamia along with Chanaranges and Mermeroes. He was executed by Khosrow shortly after his accession for plotting with other nobles to overthrow him in favor of his brother Zames.

To curb the power of the over-mighty generalissimo, Khosrow I—although this reform may already have been planned by his father, Kavadh I (r. 499–531)—split the office of the Ērān-spāhbed into four regional commands, corresponding to the four traditional cardinal directions (kust, cf. Šahrestānīhā ī Ērānšahr): the "army chief of the East (Khurasan)" (kust ī khwarāsān spāhbed), the "army chief of the South" (kust ī nēmrōz spāhbed), the "army chief of the West" (kust ī khwarbārān spāhbed), and the "army chief of Azerbaijan" (kust ī Ādurbādagān spāhbed, where the northwestern province of Azerbaijan substitutes the term "north" because of the latter's negative connotations). The exact geographical definition of each command has been retrieved from Anania Shirakatsi's Geography. As this reform was mentioned only in later literary sources, the historicity of this division, or its survival after Khosrow I's reign, was questioned in the past, but a series of thirteen recently discovered seals, which provide the names of eight spāhbeds, provide contemporary evidence from the reigns of Khosrow I and his successor, Hormizd IV (r. 579–590); P. Pourshariati suggests that two may date to the reign of Khosrow II (r. 590–628). The eight known spāhbeds are:

Other holders of the rank are difficult to identify from the literary sources, since the office of spāhbed was held in tandem with other offices and titles, such as Shahrwarāz ("Boar of the Empire"), which are often treated as personal names. A further factor of confusion in later literary sources is the interchangeable use of the rank with the junior provincial ranks of marzbān ("frontier-warden, margrave") and pāygōsbān ("district guardian").