Celsus was a 2nd-century Greek philosopher and opponent of early Christianity. His literary work, The True Word, survives exclusively in quotations from it in Contra Celsum, a refutation written in 248 by Origen of Alexandria. The True Word is the earliest known comprehensive criticism of Christianity.

Criticism of Christianity has a long history which stretches back to the initial formation of the religion in the Roman Empire. Critics have challenged Christian beliefs and teachings as well as Christian actions, from the Crusades to modern terrorism. The arguments against Christianity include the suppositions that it is a faith of violence, corruption, superstition, polytheism, homophobia, bigotry, pontification, abuses of women's rights and sectarianism.