Scylax of Caryanda (Ancient Greek: Σκύλαξ ὁ Καρυανδεύς; fl. 510s BCE) was a Greek explorer and writer of the Achaemenid Empire during the late 6th and early 5th centuries BCE. His writings are lost, though occasionally they cited or quoted by later Greek and Roman authors. The periplus sometimes referred to as the Periplus of Scylax is, in fact, not written by him. More accurately called the Periplus of Pseudo-Scylax, it was written in about the early 330s BCE by an unknown author working in the ambit of the post-Platonic Academy or the Aristotelian Peripatos (Lyceum) at Athens.

Scylax was from Caryanda, a small city on an island close to Iasos in Asia Minor. He was probably an ethnic Carian, who might have been familiar with Greek and used it for his writings. Not much is known about Scylax, except for the few fragments of information relayed by later Greek writers. Herodotus calls him a sea-captain from Ionia. He is said to have sailed down the Indus River at the behest of the Achaemenid emperor Darius I (522–486 BCE) and then around the Arabian peninsula to reach Suez. In the narrative of Herodotus:

Darius was the discoverer of the greater part of Asia. Wishing to know where the Indus (the only river with crocodiles, save one) ran into the sea, he sent a number of men, on whose trustworthiness he could rely, and among them Scylax of Caryanda, to sail down the river. They set out from the city of Caspatyrus, in the region called Pactyica, and sailed downstream in an easterly direction to the sea. Here they turned westward, and after a voyage of thirty months, reached the place from which the Egyptian king ... sent the Phoenicians to sail round Libya. Once the voyage was completed, Darius conquered the Indians, and made use of the sea in those parts. Thus all Asia, except the eastern section, has been found to exhibit the same features as Libya. (Herodotus, Histories 4.44)

Several questions have been raised about this narrative. The city of Caspatyrus and the country of Pactyica have not been traced to any real locations. Assuming that it is somewhere in the vicinity of Gandhara, which was under the control of the Achaemenid emperor, it is unclear how Scylax was able to assemble a fleet of vessels in this land-locked country. More importantly, the Indus does not flow east, but rather in a south-westerly direction. Due to these reasons, some commentators doubted if Scylax's journey ever took place.

Scholars have constructed various explanations for these questions. David Bivar has noted that 'Caspatyrus' was written as 'Caspapyrus' by the later Greek writer Hekataios, and both the names seem to have been misspellings of 'Paskapyrus', a known Greek spelling of the name of Peshawar. Scylax is presumed to have started by sailing east along the Kabul River and turned south after its confluence with the Indus River near Attock. The idea that the Indus itself flowed east must have been a misunderstanding by Herodotus or his source.

Scholars state that Scylax's expedition was not merely for exploration, but rather for reconnaissance for future conquest by Darius. According to Matthew R. Christ and Grant Parker, "Herodotus presents geographical curiosity as a feature of foreign kings, particularly when they plan conquest". Olmstead characterised it as a "spying" expedition. It lasted thirty months. Soon afterwards, Darius seems to have added to his empire the lands explored by Scylax as a new province called Hinduš. It was referred to as "India" by the Greek writers. The extent of the province is not precisely known, though Herodotus's description of it as lying to the west of the desert (Thar Desert) limits it to essentially Sindh (middle and lower Indus basin).

Darius also commissioned the completion of the canal connecting the Nile with the Red Sea, stating in an inscription:

I commanded to dig this canal from the Nile...to the sea which goes from Persia; afterwards this canal [was dug] thus as I commanded, and [ships] passed from Egypt by this canal to Persia as was my [will].