A "free church" is a Christian denomination or independent church that is intrinsically separate from government (as opposed to a theocracy, or an "established" or state church). A free church does not define government policy, and a free church does not accept church theology or policy definitions from the government. A free church also does not seek or receive government endorsements or funding to carry out its work. The term is especially relevant in countries with established state churches.
The free church model is historically what the Christian church was before the Emperor Constantine legalized Christianity (see Early Christianity) and before the later setting up of the state church of the Roman Empire.
Groups like the Waldensians were in practice free churches. In 16th century Europe, within the radical movements such as the Anabaptists were free churches with small exceptions like the Münster Rebellion. Mennonites, the Amish, the Quakers and other churches maintain free church polities into the present date both in Europe and in North America.
Free churches also evolved in the USA supported by the official separation of church and state, while much of Europe maintains some government involvement in religion and churches via taxation to support them and by appointing ministers and bishops etc., although free churches have been founded in Europe outside of the state system 
A number of churches in Scotland and Northern Ireland, mainly of the Presbyterian tradition, have used the name 'Free Church'. The most important of these to persist at the present time is the Free Church of Scotland.
Among the Methodist Churches, calling a church "free" does not indicate any particular relation to a government. Rather the Free Methodist Church is so called because of three, possibly four, reasons, depending on the source referenced. The word "Free" was suggested and adopted because the new church was to be an anti-slavery church (slavery was an issue in those days), because pews in the churches were to be free to all rather than sold or rented (as was common), and because the new church hoped for the freedom of the Holy Spirit in the services rather than a stifling formality. However, according to World Book Encyclopedia, the third principle was "freedom" from secret and oathbound societies (in particular the Freemasons).
Denominations belonging to the International Federation of Free Evangelical Churches trace their roots to the Radical Pietist movement. Radical Pietists separated from the Lutheran Churches, which held the status of state churches in Europe.
In the United States, because of the First Amendment forbidding the government establishment of religion, all churches are by definition free churches. However, many churches in the United States have requested tax-exempt status under section 501c3 of the Internal Revenue Code. This subjects the churches to certain additional regulations to maintain the tax exemption. Churches that are structured under 501(c)(3) face restrictions in the area of political speech: no substantial part of the church's activities may consist of carrying on propaganda or otherwise attempting to influence legislation. A 501(c)(3) organization is also restricted from participating or intervening in any political campaign for or against any political candidate.
In Germany, Protestant churches outside the Evangelical Church in Germany are put under a common label of, and collectively referred to, as "free churches" (Freikirchen) or "Protestant free churches" (Evangelische Freikirchen). This includes relatively new denominations like Baptists, Methodists, etc., as well as older ones like the Mennonites and Evangelical Lutheran Free Church (Germany).
In Sweden, the term Free Church (Swedish: frikyrka) often means any Christian Protestant denomination that is not part of the Church of Sweden, which was the Swedish state church up to 1 January 2000. This includes Baptists, Pentecostals, Methodists etc.