Freedom of religion is a principle that supports the freedom of an individual or community, in public or private, to manifest religion or 
belief in teaching, practice, worship, and observance. It also includes the freedom to change one's religion or beliefs.
Freedom of religion is considered by many people and most of the nations to be a fundamental human right. In a country with a state religion, freedom of religion is generally considered to mean that the government permits religious practices of other sects besides the state religion, and does not persecute believers in other faiths. Freedom of belief is different. It allows the right to believe what a person, group or religion wishes, but it does not necessarily allow the right to practice the religion or belief openly and outwardly in a public manner, a central facet of religious freedom.
Historically, freedom of religion has been used to refer to the tolerance of different theological systems of belief, while freedom of worship has been defined as freedom of individual action. Each of these have existed to varying degrees. While many countries have accepted some form of religious freedom, this has also often been limited in practice through punitive taxation, repressive social legislation, and political disenfranchisement. Compare examples of individual freedom in Italy or the Muslim tradition of dhimmis, literally "protected individuals" professing an officially tolerated non-Muslim religion.
In Antiquity, a syncretic point of view often allowed communities of traders to operate under their own customs. When street mobs of separate quarters clashed in a Hellenistic or Roman city, the issue was generally perceived to be an infringement of community rights.
Cyrus the Great established the Achaemenid Empire ca. 550 BC, and initiated a general policy of permitting religious freedom throughout the empire, documenting this on the Cyrus Cylinder.
Some of the historical exceptions have been in regions where one of the revealed religions has been in a position of power: Judaism, Zoroastrianism, Christianity and Islam. Others have been where the established order has felt threatened, as shown in the trial of Socrates in 399 BC or where the ruler has been deified, as in Rome, and refusal to offer token sacrifice was similar to refusing to take an oath of allegiance. This was the core for resentment and the persecution of early Christian communities.
Freedom of religious worship was established in the Buddhist Maurya Empire of ancient India by Ashoka the Great in the 3rd century BC, which was encapsulated in the Edicts of Ashoka.
Greek–Jewish clashes at Cyrene in 73 AD and 117 AD and in Alexandria in 115 AD provide examples of cosmopolitan cities as scenes of tumult.
The Romans tolerated most religions, including Judaism and encouraged local subjects to continue worshipping their own gods. They did not however, tolerate Christianity until it was legalised by the Roman emperor Galerius in 311. The Edict of Milan guaranteed freedom of religion in the Roman Empire until the Edict of Thessalonica in 380, which outlawed all religions except Christianity.
