Sīstān (Persian: سیستان‎) is a historical region in eastern Iran (Sistan and Baluchestan Province), southern Afghanistan (Nimruz, Kandahar and Zabul provinces).

Sistan was once the homeland of Sakas, a Scythian tribe of Iranic origin. The Saffarids, one of the early Iranian dynasties of the Islamic era, were originally from Sistan.

Sistan derives its name from Sakastan, which Sistan was once the westernmost part of. The name Sakastan, on its part, derives from Old Persian zaranka ("waterland"; cf. Pashto dzaranda). This older form is also the root of the name Zaranj, capital of the Afghan Nimruz Province.

Encyclopædia Iranica says "The name of the country and its inhabitants is first attested as Old Persian z-r-k (i.e., Zranka) in the great Bīsotūn (q.v. iii) inscription of Darius I (q.v.; col. I l. 16), apparently the original name. This form is reflected in the Elamite (Sir-ra-an-qa and variants), Babylonian (Za-ra-an-ga), and Egyptian (srng or srnḳ) versions of the Achaemenid royal inscriptions, as well as in Greek Zarángai, Zarangaîoi, Zarangianḗ (Arrian; Isidore of Charax), and Sarángai (Herodotus) and in Latin Zarangae (Pliny). Instead of this original form, characterized by non-Persian z (perhaps from proto-IE. palatal *γ or *γh), in some Greek sources (chiefly those dependent upon the historians of Alexander the Great, q.v.) the perhaps hypercorrect Persianized variant (cf. Belardi,p. 183) with initial d-, *Dranka (or even *Dranga?), reflected in Greek Drángai, Drangḗ, Drangēnḗ, Drangi(a)nḗ (Ctesias; Polybius; Strabo; Diodorus; Ptolemy; Arrian; Stephanus Byzantius) and Latin Drangae, Drangiana, Drangiani (Curtius Rufus; Pliny; Ammianus Marcellinus; Justin) or Drancaeus (Valerius Flaccus, Argonautica 6.106, 6.507) occurs."