According to the Dutch linguist Robert S. P. Beekes, the name predates Greek presence in the region and could come from the Pre-Greek form reconstructed as *Kʷʰeťťal-.

[5] The Greek linguist Georgios Babiniotis also assigns the origin of the name of the Thessalians to pre-Greek times, although he does not try to explain its etymology.

[7] In Homer's epic, the Odyssey, the hero Odysseus visited Aeolia, the kingdom of Aeolus, which was the old name for Thessaly.

Thessaly was home to extensive Neolithic and Chalcolithic cultures around 6000–2500 BC (see Cardium pottery, Dimini and Sesklo).

In Archaic and Classical times, the lowlands of Thessaly became the home of baronial families, such as the Aleuadae of Larissa or the Scopads of Crannon.

The Greek army that guarded the Vale of Tempe was alerted by Alexander I of Macedon and evacuated the road before the enemy arrived.

The following year, the Persians were decisively defeated at the Battle of Plataea and withdrew from all of their European possessions, including Thessaly.

[11] In the 4th century BC, after the Greco-Persian Wars had long ended, Jason of Pherae transformed the region into a significant military power, recalling the glory of Early Archaic times.

In the 7th century the Avar-Slav alliance began to raid the Byzantine Empire, laying siege to Thessalonica and even the imperial capital Constantinople itself.

By the 8th century, Slavs had occupied most of the Balkans from Austria to the Peloponnese, and from the Adriatic to the Black seas, with the exception of the coastal areas and certain mountainous regions of the Greek peninsula.

With the abatement of Arab-Byzantine Wars, the Byzantine Empire began to consolidate its power in those areas of mainland Greece occupied by Proto-Slavic tribes.

[20] In return, many Greeks from Sicily and Asia Minor were brought to the interior of Greece, to increase the number of defenders at the Emperor's disposal and dilute the concentration of Slavs.

In 1066 dissatisfaction with the taxation policy led the Aromanian and Bulgarian population of Thessaly to revolt against the Byzantine Empire under the leadership of a local lord, Nikoulitzas Delphinas.

[22] In 1199–1201 another unsuccessful revolt was led by Manuel Kamytzes, son-in-law of Byzantine emperor Alexios III Angelos, with the support of Dobromir Chrysos, the autonomous ruler of Prosek.

[23] Following the siege of Constantinople and the dissolution of the Byzantine Empire by the Fourth Crusade in April 1204, Thessaly passed to Boniface of Montferrat's Kingdom of Thessalonica in the wider context of the Frankokratia.

[27] The Vlachs (Aromanians) of Thessaly (originally a chiefly transhumant Romance-speaking population)[28][29] first appear in Byzantine sources in the 11th century, in the Strategikon of Kekaumenos and Anna Komnene's Alexiad).

The term is also used by the 13th-century scholar George Pachymeres, and it appears as a distinct administrative unit in 1276, when the pinkernes Raoul Komnenos was its governor (kephale).

[32] In 1318, with the death of John II, Thessalian independence came to an end, and the Almogavars occupied Siderokastron and southern Thessaly (1319) and formed the Duchy of Neopatria.

[36] The Albanian tribes of Bua, Malakasioi and Mazaraki were described as "unruly" nomads living in the mountains of Thessaly in the early 14th century in Emperor John VI Kantakouzenos’ ‘History’.

Two of their military leaders known in Byzantine sources as Peter and John Sebastopoulos controlled the small towns of Pharsala and Domokos.

Simeon's son John Uroš succeeded in 1370 but abdicated in 1373, and Thessaly was administered by the Greek Angeloi-Philanthropenoi clan until the Ottoman conquest c. 1393.

Nevertheless, Ottoman control was threatened throughout this era by groups of Greeks, Albanians and Aromanians who based themselves in the mountainous areas of Thessaly.

[40] At the time of the Ottoman conquest, the great Eastern plain of Thessaly was almost entirely depopulated as a result of the nearly continuous warfare of the previous decades.

[43] Thessaly became part of the modern Greek state in 1881, after the Convention of Constantinople except the area around the town of Elassona, which remained in Ottoman hands until 1912.

The northern tier of Thessaly is defined by a generally southwest-northeast spur of the Pindus range that includes Mount Olympus, close to the Macedonian border.

Thessaly's major river, the Pineios, flows eastward from the central Pindus Range just south of the spur, emptying into the Thermaic Gulf.

[49] The alluvial soils of the Pineios Basin and its tributaries make Thessaly a vital agricultural area, particularly for the production of grain, cattle, and sheep.

Thessaly is the leading cattle-raising area of Greece, and Aromanian shepherds move large flocks of sheep and goats seasonally between higher and lower elevations.

The nearly landlocked Gulf of Pagasai provides a natural harbor at Volos for shipping agricultural products from the plains and chromium from the mountains.

The region is directly linked to the rest of Europe through the International Airport of Central Greece, which is located in Nea Anchialos, a small distance from Volos and Larisa.