Thasos (Greek: Θάσος [ˈθas̠os̠]) is a Greek island in the northern Aegean Sea. It is the northernmost major Greek island, and 12th largest by area.

The island has an area of 380 km² and a population of about 13,000. It forms a separate regional unit within the East Macedonia and Thrace region. Before the local administration reform of 2011, it was part of the Kavala Prefecture. The largest town and the capital is Thasos, officially known as Limenas Thasou, "Port of Thasos", situated on the northern side. It is connected with the mainland by regular ferry lines between Keramoti and Thasos town, and between the regional centre of Kavala and Skala Prinou.

The most important economic activity on the island is tourism. The main agricultural products are honey, almonds, walnuts, olives (such as the local Throumba variety which has a protected designation of origin), olive oil, and wine. The inhabitants also engage in fishing, and in the herding of sheep and goats.

Staphylus (Ancient Greek: Στάφυλος), the beloved son of god Dionysus, lived in Thasos.

Lying close to the coast of Eastern Macedonia, Thasos was inhabited from the Palaeolithic period onwards, but the earliest settlement to have been explored in detail is that at Limenaria, where remains from the Middle and Late Neolithic relate closely to those found at the mainland's Drama plain. In contrast, Early Bronze Age remains on the island align it with the Aegean culture of the Cyclades and Sporades, to the south; at Skala Sotiros for example, a small settlement was encircled by a strongly built defensive wall. Even earlier activity is demonstrated by the presence of large pieces of 'megalithic' anthropomorphic stelai built into these walls, which, so far, have no parallels in the Aegean area.

There is then a gap in the archaeological record until the end of the Bronze Age c 1100 BC, when the first burials took place at the large cemetery of Kastri in the interior of the island. Here built tombs covered with small mound of earth were typical until the end of the Iron Age. In the earliest tombs were a small number of locally imitated Mycenaean pottery vessels, but the majority of the hand-made pottery with incised decoration reflects connections eastwards with Thrace and beyond.

The island was colonised at an early date by Phoenicians, attracted probably by its gold mines; they founded a temple to the god Melqart, whom the Greeks identified as "Tyrian Heracles", and whose cult was merged with Heracles in the course of the island's Hellenization. In the 5th century BC, Herodotus visited a sanctuary of Heracles on Thasos, presumably the Heracleion still visible today, and reported that it had been built by the Phoenicians. An eponymous Thasos or Thasus, son of Phoenix (or of Agenor, as Pausanias reported) was said to have been the leader of the Phoenicians, and to have given his name to the island.

Around 650 BC, or a little earlier, Greeks from Paros founded a colony on Thasos. A generation or so later, the poet Archilochus, a descendant of these colonists, wrote of casting away his shield during a minor war against an indigenous Thracian tribe, the Saians. Thasian power extended to the mainland, where the Thasians owned gold mines even more valuable than those of the island; their combined annual revenues amounted to between 200 and 300 Attic talents. Herodotus says that the best mines on the island were those opened by the Phoenicians on the east side, facing Samothrace. Archilochus described Thasos as "an ass's backbone crowned with wild wood." The island's capital, Thasos, had two harbours. Besides its gold mines, the wine, nuts and marble of Thasos were well known in antiquity. Thasian wine was quite famous. Thasian coinage bore images of the wine-god Dionysos and grape bunches.