Filiki Eteria (Greek: Φιλικὴ Ἑταιρεία, romanized: Filikī́ Etaireía) or Society of Friends (Greek: Ἑταιρεία τῶν Φιλικῶν, romanized: Etaireía tôn Filikôn) was a secret political and revolutionary organization founded in 1814 in Odessa, whose purpose was to overthrow Ottoman rule in Greece and establish an independent Greek State. Society members were mainly young Phanariot Greeks from Constantinople and the Russian Empire, local political and military leaders from the Greek mainland and islands, as well as several Orthodox Christian leaders from other nations that were under Hellenic influence, such as Karađorđe from Serbia, and Tudor Vladimirescu from Romania. One of its leaders was the prominent Phanariote Prince Alexander Ypsilantis. The Society initiated the Greek War of Independence in the spring of 1821.

The direct translation of the word "Φιλική" is "Friendly" and the direct translation of "Ἑταιρεία" is "Society", "Company" or "Association"). The common transliteration "Filiki Eteria" reflects the pronunciation of the name in modern Greek. Other possible transliterations are "Filike Etaireia", which reflects Greek orthography, and "Philike Hetaireia", which reflects the ancient Greek etymology. The word "friendly" here is meant to connote allies who work towards the same goal, not necessarily those who socialize together.

In the context of ardent desire for independence from Turkish occupation, and with the explicit influence of similar secret societies elsewhere in Europe, three Greeks came together in 1814 in Odessa to decide the constitution for a secret organization in freemasonic fashion. Its purpose was to unite all Greeks in an armed organization to overthrow Turkish rule. The three founders were Nikolaos Skoufas from the Arta province, Emmanuil Xanthos from Patmos and Athanasios Tsakalov from Ioannina. Soon after they initiated a fourth member, Panagiotis Anagnostopoulos from Andritsaina.

Skoufas met with Konstantinos Rados, who was initiated into Carbonarism. Xanthos was initiated into a Freemasonic Lodge at Lefkada ("Society of Free Builders of Saint Mavra"), while Tsakalov was a founding member of the Hellenoglosso Xenodocheio (Greek: Ελληνόγλωσσο Ξενοδοχείο, meaning Greek-speaking Hotel) an earlier relative society for the liberation of Greece which had been founded in Paris and made a progress to the Greek nationalistic ideas.

At the start, between 1814 and 1816, there were roughly twenty members. During 1817, the society initiated members from the diaspora Greeks of Russia and the Danubian Principalities of Moldavia and Wallachia. The Prince of Moldavia Michael Soutzos himself, became a member. Massive initiations began only in 1818 and by early 1821, when the Society had expanded to almost all regions of Greece and throughout Greek communities abroad, the membership numbered in thousands. Among its members were tradesmen, clergy, Russian consuls, Ottoman officials from Phanar and revolutionary Serbs, most notably, the leader of the Serbian Revolution, father of the modern Serbia and founder of the Karadjordjevic dynasty Karageorge Petrovic. Members included primary instigators of the Greek revolution, notably Theodoros Kolokotronis, Odysseas Androutsos, Dimitris Plapoutas, Papaflessas and the metropolitan bishop Germanos of Patras.

Filiki Eteria was strongly influenced by Carbonarism and Freemasonry. The team of leaders made and spread its decisions, saying that they transmitted the commands of an "Invisible Authority" (Αόρατος Αρχή), who was thought to be one or more strong persons, so that from the start it was shrouded in mystery, secrecy and glamour. It was generally believed that a lot of important personalities were members, not only eminent Greeks, but also notable foreigners such as the Tsar of Russia Alexander I. The reality was that initially, the Invisible Authority comprised only the three founders. From 1815 until 1818, five more were added to the Invisible Authority, and after the death of Skoufas three more. In 1818, the Invisible Authority was renamed to the "Authority of the Twelve Apostles" and each Apostle shouldered the responsibility of a separate region.

The organisational structure was pyramid-like, with the "Invisible Authority" coordinating from the top. No one knew or had the right to ask who created the organisation. Commands were carried out unquestioningly and members did not have the right to make decisions. Members of the society came together in what was called a "Temple" with four levels of initiation: a) Brothers (Αδελφοποίητοι) or Vlamides (Βλάμηδες), b) the Recommended (Συστημένοι), c) the Priests (Ιερείς) and d) the Shepherds (Ποιμένες). The Priests were charged with the duty of initiation.

I swear in the name of truth and justice, before the Supreme Being, to guard, by sacrificing my own life, and suffering the hardest toils, the mystery, which shall be explained to me and that I shall respond with the truth whatever I am asked.