Christians in Iraq are one of the oldest, continuous and significant Christian communities. The vast majority of Iraqi Christians are indigenous Assyrians who descend from the ancient Assyria, followed by Armenians and Arab Christians, and a very small minority of Kurdish, Shabaks and Iraqi Turkmen Christians. Christians in Iraq primarily adhere to the Syriac Christian tradition and rites and speak Northeastern Neo-Aramaic dialects, although Turoyo is also present on a smaller scale. Some are also known by the name of their religious denomination as well as their ethnic identity, such as Chaldean Catholics, Chaldo-Assyrians, or Syriacs. Regardless of religious affiliation (Chaldean Catholic Church, Assyrian Church of the East, Syriac Orthodox Church, Syriac Catholic Church, Assyrian Pentecostal Church, etc.) Assyrians Christians in Iraq and surrounding countries are one genetically homogeneous people and are of different origins than other groups in the country, with a distinct history of their own harking back to ancient Assyria and Mesopotamia.

Christians have inhabited modern-day Iraq for about 2,000 years, tracing their ancestry to ancient Mesopotamia and surrounding lands. The great patriarch Abraham came from Ur (modern-day Nasiriyah), while Isaac's wife Rebecca came from Assyria (in modern-day northwestern Iraq.) Additionally, Daniel lived in Iraq most of his life and the prophet Ezekiel was from southern Iraq and his shrine is located there. Shrines of the prophet Jonah and Saint George are also located there, and a number of other biblical prophets and saints are said to have been from there as well. Adam and Eve are also widely thought to have hailed from Iraq, as the biblical Garden of Eden is often believed to have been located in southern Iraq. Syriac Christianity was first established in Mesopotamia, and certain subsets of that tradition (namely the Church of the East and its successor churches) were established in northern and central-southern Iraq. This would become one of the most popular Christian churches in the Middle East and Fertile Crescent and would spread as far east as India and China.

Prior to the Gulf War in 1991, Christians numbered one million in Iraq. This may be an underestimate by half as seen in the 1987 census numbers. Saddam Hussein kept anti-Christian violence under control but Christians were subjected some to "relocation programmes". The predominantly ethnically and linguistically distinct Assyrians were pressured to identify as Arabs. The Christian population fell to an estimated 800,000 during the Iraq War. During the 2013–2017 Iraq War with ISIS rapidly sweeping through western lands, Christian fled as they feared the persecution by the militants, as they were to "execute" any person who did not believe in their Sunni sect. Thousands of Christians fled to Baghdad, where they found refuge and adequate housing, some of whom have chosen to make Baghdad their new permanent home following the full defeat of ISIS in Iraq. Thousands have also fled to other parts of southern Iraq, such as the Shia-majority city of Najaf which housed thousands of Christians in holy Islamic shrines once they fled from ISIS. A large population have also returned to their homes en masse following the defeat of ISIS and were able to celebrate Christian festivals in safety with the protection of the Nineveh Plain Protection Units and its allies. The current number of Assyrians is said to be less than 140,000 in 2024, according to the non-profit Shlama Foundation. Based on broader religious identification, the number of Christians is likely only slightly larger.

Christians in Iraq have been well-integrated and have contributed greatly to Iraq, popularly as scholars, researchers, academics, and economists. Iraqi Christians have also hold high positions in the government, such as Thabit AbdulNour and Tariq Aziz. There is a large population that are entertainers, artists, actresses and singers.

Christianity in Iraq has its roots in the conception of the Church of the East in the 5th century AD, predating the existence of Islam in the region of Iraq. Iraqi Christians are predominantly native Assyrians belonging to the Ancient Church of the East, Assyrian Church of the East, Assyrian Pentecostal Church, Assyrian Evangelical Church, Mar Thoma Church, Chaldean Catholic Church, Syriac Catholic Church and Syriac Orthodox Church. In Iraq, there is also a significant population of Armenian Christians whose ancestors had fled from Turkey during the Armenian genocide. The Christian population increased from 550,000 in 1947 (12% of the population of 4.6 million) to 1.4 million in 1987 (8% of the estimated population of 16.3 million). After the 2003 invasion of Iraq, violence against Christians increased, with reports of abduction, torture, bombings, and killings. The Iraq War (2003-2011) displaced much of the remaining Christian community from their homeland as a result of ethnic and religious persecution at the hands of Islamic extremists.

Christianity was brought to Iraq in the 1st century by Thomas the Apostle and Mar Addai (Addai of Edessa) and his pupils Aggai and Mari. Thomas was one of the Twelve Apostles while, according to tradition, Addai was one of the first 70 disciples. Iraq's Eastern Aramaic-speaking Assyrian communities are believed to be among the oldest in the world.

The Assyrian people adopted Christianity in the 1st century and modern-day northern Iraq became the centre of Eastern Rite Christianity and Syriac literature from the 1st century until the Middle Ages. Among the Assyrians, Christianity initially co-existed with the ancient Mesopotamian religion until the latter began to decline in the 4th century.

In the early centuries after the Arab Islamic conquest of the 7th century, Assyria (also known as Athura and Asoristan) was dissolved by the Arabs as a geopolitical entity. However, the indigenous Assyrians (known as Ashuriyun by the Arabs) continued to play an influential role in Iraq as scholars and doctors.