The word "Unitarian" historically refers to the oneness of God as opposed to the Trinity of God, belief in which is referred to as"Trinitarianism".

The word Trinity is not in the Bible, nor is the concept. The naming of Father Son and Holy Spirit hardly occurs, except as a echo of a baptismal formula. The doctrine dates from the early Middle Ages, as an effort to reconcile Jewish theology with Greek philosophy, and was adopted as doctrine at the Council of Nicea in 325 AD at the behest of Constantine. The leader of the Trinitarian position was St. Nicholas (later known as Santa Claus), who later actively persecuted Unitarians.

At that time the Unitarian position was called "Arianism" for its leader Arius of Alexandria. He and the idea were declared heretic, and was crushed except for a few remote Germanic tribes.

With the invention of the printing press in the 1450's, and the wide reading of the Bible, people discovered that the Trinity was not there, and Unitarians (often called Arians) sprang up all over Europe like crocus. In most places they were killed. Calvin burned the best known Renaissance Unitarian theologian, the Spaniard Servetus, in Geneva, in 1604. He was burned with a slow fire, taking half an hour to kill him, with his books and writings strapped to him. Earlier he had been burned in effigy by Catholics. (Servetus was also a doctor, and had discovered the pulmonary circulation of the blood.)

Many early Unitarians tended to be scientists or doctors. The Polish king's doctor was Unitarian, and Krakow (the early capital), became one of the few places Unitarians were allowed to live without being killed. They formed a convocation in 1565. After the Counter Reformation began to gain strength, and they were less welcome in Krakow, they gathered from all over Europe in a town they established near Krakow (Rakow), establishing a university and printing press, under the leadership of the Italian theologian Socinus. Books were smuggled to England, and Unitarianism took root there.

With a change in the throne (as with Bloody Mary in England) Unitarians in Poland had in 1660 to choose between death, becoming Catholic, or fleeing. (Some in Hungary become Jewish since Jews were infidels rather than heretics, and were not being put to death). Those would could afford the move fled by wagon to Transylvania (near the border with Islam), losing all they possessed to Hungarian attacks as they crossed. Transylvania is the only area with Unitarian church buildings more than 500 years old are still in use by Unitarians. (Structures still exist in Poland, but have been put to other uses.) The Communist government was in the process of destroying those in Transylvania when it fell.

Some Polish Unitarians managed to reach The Netherlands, where the printing press was reestablished, and Unitarian books republished. These were largely in Latin, so could be read by the educated all over Europe. Titles smuggled into England planted the seed of Unitarianism there. Unitarianism has always been a movement of books rather than missionaries.

Unitarianism came to America among the Pilgrims, and separated from Congregationalism in New England the early 19th century. You can tell which won the vote in each New England town; in some towns the Congregational building is the older, in others the Unitarian.

Unitarianism came to Canada from Britain, Ireland and Iceland, and in some churches, there were Icelandic services into living memory.

Emerson was the first American Unitarian minister to have major influence on European Unitarianism. Benjamin Franklin, Thomas Jefferson, Tom Paine, Henry David Thoreau, Clara Barton, and Adlai S Stevenson were among American Unitarians, or have been claimed by Unitarianism as being in harmony with Unitarian thought of their time. Albert Schweitzer accepted Unitarian membership.

In the 1930's American Unitarianism almost split between the Theists (those who believe in a personal god), and Humanists (who see human values as paramount). This argument has largely vanished today. In each congregation now you will find both, as well as those who manage to hold both positions simultaneously, as well as other concepts of ultimate reality.

Those who entered Unitarianism in the past generation were primarily "come outers" from more traditional traditions, and were in rebellion against what they regarded as superstitions. Young adults now coming to Unitarianism (often seeking a church school for their children) are more likely to be coming from a secular background and to be seeking spiritual meaning. While humanism remains in first place numerically among Unitarians, those with an "Earth/Nature" centred concept of ultimate reality are now in second place as opposed to the earlier Deists (God made the world but now leaves it alone, the concept of Franklin and Jefferson among others), or Theists.

These all have in common the idea that values are more important than belief, optimism about the nature of humankind, and valuing the use of reason. It has been said that Unitarians can tolerate anything except intolerance.

Unitarianism is the first non gay denomination to ordain women and gays to ministry, and to perform gay weddings. They are not an historic peace church, but they joined Quakers and Mennonites in opposing the war in Vietnam, and later Iraq. Social action is an important part of the life of the denomination. The first white man killed in the U.S. southern civil rights movement was a Unitarian minister.

Unitarians tend to be more alike in their value system across socioeconomic and geographic lines, but differ in beliefs. Other denominations, from Catholic to Baptist, tend to hold the same beliefs across socioeconomic and geographical lines, but have widely differing values. It is in the commonality of values that we find our community.

We are a do-it-yourself religion. To be Unitarian you have to work at it. You have to use your mind.

The certainly of dogma, be it Communist, secular humanism, fundamentalist Christian, extreme patriotism, or Islamic fundamentalism, has its appeal. All the answers are given to you. All you have to do is accept, believe, and have faith. Dogma gives you a complete world view, and an understanding of your place in the world.

Unitarians on the other hand are never certain of having the final answers. We have set of values. We are optimistic about our ability to apply those values to the complexities of our world, and arrive at our own answers concerning right and wrong and appropriate actions. This takes work. While it keeps us small, we have had influence beyond our numbers.