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

In the early years of Christianity, the Neoplatonic philosopher Porphyry emerged as one of the major critics with his book Against the Christians, along with other writers like Celsus and Julian. Porphyry argued that Christianity was based on false prophecies that had not yet materialized. Following the adoption of Christianity by the Roman Empire, dissenting religious voices were gradually suppressed by both governmental and ecclesiastical authorities. Christianity has faced significant theological criticism from thinkers of other Abrahamic religions, particularly including Judaism and Islam. Notably, Maimonides, the renowned rabbi, Jewish philosopher, and Torah scholar of the 12th century, argued that Christian practices and doctrines constituted idolatry and deviated from the strict monotheism (shituf) of Jewish and Muslim theologies. Similarly, Islamic scholars have critiqued Christian beliefs about the Trinity and the divinity of Jesus, viewing these concepts as incompatible with the concept of monotheism. These critiques reflect deep theological disagreements rooted in their shared scriptural traditions and divergent doctrinal interpretations. A millennium later, the Protestant Reformation led to a fundamental split in European Christianity and rekindled critical voices about the Christian faith, both internally and externally. In the 18th century, deist philosophers such as Voltaire and Jean-Jacques Rousseau were critical of Christianity as a revealed religion. With the Age of Enlightenment, Christianity was criticized by major thinkers and philosophers, such as David Hume, Thomas Paine, and the Baron d'Holbach. The central theme of these critiques sought to negate the historical accuracy of the Christian Bible and focused on the perceived corruption of Christian religious authorities. Other thinkers, like Immanuel Kant, offered critiques of traditional arguments for the existence of God, while professing to defend Christian theology on novel grounds.

In modernity, Christianity has faced substantial criticism from a wide array of political movements and ideologies. In the late eighteenth century, the French Revolution saw a number of politicians and philosophers criticizing traditional Christian doctrines, precipitating a wave of secularism in which hundreds of churches were closed and thousands of priests were deported or killed. Following the French Revolution, prominent philosophers of liberalism and communism, such as John Stuart Mill and Karl Marx, criticized Christian doctrine on the grounds that it was conservative and anti-democratic. Friedrich Nietzsche wrote that Christianity fosters a kind of slave morality that suppresses the desires contained in the human will. The Russian Revolution, the Chinese Communist Revolution, and several other modern revolutionary movements have also led to the criticism of Christian ideas.

Christians' formal response to such criticisms is described as Christian apologetics. Philosophers like Augustine of Hippo and Thomas Aquinas have been some of the most prominent defenders of the Christian religion since its foundation.

Biblical criticism, in particular higher criticism, covers a variety of methods which have been used since the Age of Enlightenment in the early 18th century as scholars began to apply the same methods and perspectives which had already been applied to other literary and philosophical texts to biblical documents. It is an umbrella term that covers various techniques that mainline and liberal Christian theologians mainly use to study the meaning of biblical passages. It uses general historical principles and is primarily based on reason rather than revelation or faith. There are four primary types of biblical criticism:

Within the abundance of biblical manuscripts exist a number of textual variants. The vast majority of these textual variants are the inconsequential misspelling of words, word order variations and the mistranscription of abbreviations. Text critics such as Bart D. Ehrman have proposed that some of these textual variants and interpolations were theologically motivated. Ehrman's conclusions and textual variant choices have been challenged by some conservative evangelical reviewers like Daniel B. Wallace, Craig Blomberg, and Thomas Howe.

In attempting to determine the original text of the New Testament books, some modern textual critics have identified sections as probably not original. In modern translations of the Christian Bible, the results of textual criticism have led to certain verses being left out or marked as not original. These possible later additions include the following:

In The Text of the New Testament, Kurt and Barbara Aland compare the total number of variant-free verses, and the number of variants per page (excluding orthographic errors), among the seven major editions of the Greek New Testament (Tischendorf, Westcott-Hort, von Soden, Vogels, Merk, Bover and Nestle-Aland) concluding 62.9% (4999/7947) agreement. They concluded,