The history of Sifnos goes back a long time away, as with all Cycladic Islands.
Research estimate that the island was inhabited for the first time around the 5th millennium B.C. and that during the 3rd millennium B.C. came the first Pre-Hellenic or Aegean inhabitants.  There is evidence of a first Cycladic Civilization from the archaeological excavations of Chr.Tsounta (1898-1899). The excavations prove that during that period Sifnos had economic prosperity, as opposed to other Cycladic islands, being the center for argil and lead mining.

During the middle Cycladic period from 2000 till 1550 B.C., Cretans used the Cycladic islands as their center of commerce for their transactions with the mainland. Sifnos was also influenced and according to the history researcher Stephan Byzantio, Sifnos was supposed to have a Cretan colony called Minoa that has never been found.

From 1450 till 1100 B.C. Sifnos was influenced by the Mycenaean period and from 1130 till 1120 B.C.  the Ionians arrived on the island under the leadership of Alkinora. It was during that period that it took the name Sifnos and according to Herodotus, the ancient capital was established in Kastro under the name “Asty”. 
In the 6th century Sifnos was thriving. Herodotus remarked about the wealth of the Sifnians in his works and mentioned them as the richest of the islanders. The wealth of Sifnos came basically from the gold and argil mines and already in 600 B.C. Sifnos had its own currency. Between the 8th and 6th centuries in Asty the construction of a high wall like the acropolis began.  Inside were the prytaneum, the ancient city market, a stone temple and on the top an observation post and optical telegraphs for protection of the mineral wealth.

In 525 B.C. the inhabitants of the island gave as a present to the sacred temple of Apollo in Delphi, a unique art masterpiece, known through the centuries as the treasure of the Sifnians. It was a building of Ionian style.  The front  was supported by two Caryatids instead of pillars, and according to Paphsania it was paid for with custom duties from the mines.  Due to its wealth Sifnos continued to make various offerings to Delphi, like a golden egg for example.

In 524 B.C. political refugees, opponents of the tyrant Polycratus, arrived from Samos and when denied of any financial support by the Sifnians, they besieged and ravaged the island and finally managed to take 100 talants, a huge amount of money for that period of time. That action and the probable destruction of the mines of Aghios Sostis close to the sea shook the economy and the island fell into decline.
The Persians appeared on the island at the end of the 6th century, but the Sifnians refused to give them “earth and water” and allied with the Greeks against them in the battle of Salamina in 480 B.C. and participated with a “pentikontoro”, a wooden ship with 50 oars.
In 478-477, when the 1st Athenian Alliance was established, Sifnos joined it and paid taxes to the Athenians.
Sifnos fought on the side of the Athenians in the battle of Plateon in 479 B.C., during the Peloponnesus War and when the Athenian fought against Sicily in 415 B.C.
In 411 B.C. Pisandros imposed oligarchy on the island and in 404 B.C., after the capitulation of Athens, Sifnos surrendered to the Spartans.  
After the Corinthian Alliance the island came under Macedonian sway and with the dominance of Philip B’ and afterwards of Alexander the Great, Sifnos became a meeting place, probably because of its geographical location. During that period lived the royal doctor Diphilos, who was the personal physician of Lycimachos, the King of Thrace, and who wrote a book about diet for both healthy and sick people.

Some years later, in 334 B.C., the Persian fleet under the command of Datamis, tried a diversionary attack against Alexander the Great, but he suffered a crushing defeat by Proteus, leader of the Greek fleet. After the death of Alexander the Great Sifnos came under the power of his successors and started the fortification of the island. All construction was stopped by the arrival of Phillip the 5th of Macedonia in 202 B.C., who wanted control of the Aegean Sea. Although he wanted to destroy the local economy of the islands, he didn’t want to damage his good relation with Rhodes and so he tried to achieve this with pirate attacks. It was at the same time that the war between Crete and Rhodes began. Rhodes asked for  help from Rome. The Cretans arrived on Sifnos in 162 B.C. after using devious means and caused a lot of damages on the island.

In Roman times, Sifnos had relative independence, although not much evidence remains  from that period. Some evidence is in Kastro: the marble urns with sculpted decorations and an altar in the church of Keemisis tis Theotokou (Assumption of the Virgin Mary).
It’s worth mentioning that according to some theories, Sifnos became the place of exile for Rome’s political opponents during the last years of Roman rule.

In the Byzantine period (6th century), Sifnos was a member of the 26th Province of the islands with Rhodes as its capital. The second half of the 7th century during the Byzantine Empire’ s fragmentation, Sifnos participated in the “Theme of the Aegean Sea” with Samos as its capital. 
It’s not known when exactly Christianity appeared on the island, only its participation in the war on icons 726 – 843 A.D. Many of the supporters of the iconoclasts were intellectual people and clergymen who took shelter on the island and contributed to the spiritual and literary flourishing of Sifnos.

In 1207 A.D. Sifnos followed the same course as all the other islands in the Cyclades. During the Venetian rule and when Marcus Sanoudos was in power, the island became a member of the Duchy of Naxos.
In 1279 A.D. Sifnos was under Byzantine rule, under the leadership of admiral Likarios and constituted a Byzantine province till 1307, when the Spanish knight Giannoulis Da Coronia, of the Knights Order of Saint Johann, conquered it.
The period that the island was ruled by the House of Da Coronia (1307-1464 A.D.) was characterized on one hand by the attacks and incursions of the Venetians from Naxos who wished to re instate their power on the island and on the other hand by the attacks of Turkish pirates. 
In 1464 A.D. and after the death of the last Da Coronia, Nicolas B’ Gozadinos, from the House of Kea and Thermion took power, married Marietta Da Coronia, last heir of Da Corornia House and established a new miniature state with Kastro as its capital. The period during the rule of Gozadinon (1464-1537) was not easy and had the same luck as the previous one.  As evidence shows in 1537 Nicolas Gozadinos suffered Turkish attacks and delivered the island to the pirate, Chareidin Barbarossa. After that Sifnos was annexed to the Ottoman Empire, paying a yearly fee of about 300 ducats. 
In 1566 A.D. the sultan gave away the islands to the Jewish Bay Joseph Nazi, who ruled from a distance through his representative Francisco Koronelo. The House of Gozadinon ruled again from 1578 and after a lot of grants stayed in power until 1617.

In general Turkish domination lasted from 1537 until the revolution in 1821 and due to some grants and privileges that Sifnos had, it managed to regroup itself. The system of governing via a representative, for example, helped Sifnos to develop local administration and being a central commercial port in the Cyclades helped its financial prosperity.
The Orthodox Church was specially favoured during that period and consolidated its position firstly by establishing an Archbishopric in Sifnos in 1646 with jurisdiction in 11 islands, and secondly by setting up a high level school with professors who were catholic priests from the Vatican (1625-1634), where orthodox students attended. The church of Jerusalem gave away the Episcopacy of the Holy Sepulchre in return for the establishment of a school, known as “School of the Archipelago” (1687), where important people of literature and art studied and taught.

Between 1779 and 1774, Sifnos was under the Russian domination of the Orlov brothers and after the end of the Russian – Turkish War it went back to the Turks.

During the glorious time of the revolution in 1821, Sifnos offered a significant contribution to the common battle for the freedom of the nation. The island school’s principal, Nicolas Chrysogelos, announced the revolution by hoisting the Greek flag on the school building and together with 150 men sailed for Peloponnesus to participate in the battle. After the establishment of the Greek State by Kapodistria, Chrysogelos became Minister of Education and laid the foundation for modern (dimotiki) education.

During the Second World War (1940-1944) Sifnos, like all the other islands, suffered the consequences of Italian domination.