Before 2.000 BC: The first trace of habitation - Protohelladic tribes (Pelasgians, Leleges, Carians, Cretans) leave traces of buildings, Pelasgian walls, and the foundations of very early acropolis. - 15th century BC: Colonisation by Achaeans.
According to the myths, Herakles, returning from Troy, was shipwrecked off Kos and conquered the island after a fierce fight; this narrative indicates that the island was under Doric occupation before the Trojan War.
- ca. 1.200 BC: Kos - with Kalymnos, Karpathos, Leros, Nissyros and Kasos - sends 30 ships to the Trojan War, under Pheidippos and Antiphos of the line of Herakles (Homer, Iliad, II 622).
After the fall of Troy, Podaleirios, a renowned physician, and his comrades - all of the line of Asclepios - arrive as castaways on Kos and establish the cult of the healer-god Asklepios.
- 11th century BC: Colonisation by Dorians - Kos gains in Strength.
- 7th-6th centuries BC: The period in which, according to Plutarch, Kos was the height of its power.
- ca. 700 BC: Foundation of the Doric Hexapolis - The Doric cities of Lindos, Ialysos, Kamiros, Knidos and Halikarnassos form a holy alliance with Kos.
- Late 6th century BC: Kos is taken by the Persians and sovereignty over it is given to their ally Artemesia, queen of Halicarnassos.
- 480 BC: Battle of Salamis - defeat of the Persians.
- 477 BC: Liberation of Rhodes from the Persians - alliance with Athens - membership of the Athenian Confederation.
- 460-459 BC: The great physician Hippocrates is born on Kos.
- 431-404 BC: The Peloponnesian War.
- 411 BC: Astyochos, the Spartan admiral, destroys Astypalaia, the old main city of Kos - Some of the survivors of the disaster move to the nearby island which takes the same name of their former homeland. Other survivors found a new city at the other end of Kos, where the town still stands today.
- 357 BC: At the instigation of king Mausolos of Halicarnassos and his consort Artemesia, the democratic system of gouvernment of Kos is overthrown, with desastrous results for the cultural and economic life of the island.
- 332 BC: The Persians conquer the island - in the same year, the generals of Alexander the Great liberate it - all the Greek cities are declared independent - Kos becomes an ally of Alexander.
- 311 BC: The island is ruled by Ptolemy.
- 306 BC: Kos is captured by Antigonos.
- 301 BC: Ptolemy recaptures Kos.
- 102 BC: Cleopatra, wife of Ptolemy Euergetes, entrusts the greater part of her treasure to the Asklepieion of Kos.
- 88 BC: The people of Kos help the Romans against Mithridates of Pont, who defeats the Romans and then sacks Kos, carrying off Cleopatra's treasures.
- 82 BC: Liberation of Kos. The island makes an alliance with Rome.
- 30 BC: Complete subjugation to Rome - although sometimes granted autonomy because of the importance of the asklepieion, Kos continues to lose most of its art treasures, the works in its libraries, etc.
- Early Christian period: St Paul spreads the word of the new religion, Christianity.
- 330 AD: Kos becomes part of the theme of the Dodecanese in the Byzantine Empire - constant raids and short periods of occupation.
- 1306: The Knights of St John purchase Kos from Byzantine admiral Vinioli, its overlord - the local people put up resistance and the Knights besiege the island.
- 1309: The Knights capture Kos and rule it for 200 years.
- Mid 15th century: First Ottomans attacks.
- 1523: Sultan Suleyman captures Kos after the withdrawal of the Knights from the islands.
- 1912: Italy occupies Kos.
- 1943: Germany occupies Kos in the Second World War.
- 1945: Kos is Liberated by the Allies.
- 7 March 1948: Kos and the other islands of the Dodecanese are united with Greece.