In Christianity, angels are the messengers of God, and take on varying roles throughout the Christian Bible. They serve primarily as messengers, but also as counsellors and guides throughout the Old and New Testaments.

Psalms 91:11–12 attributes the guardianship of men to the angels.

In Matthew 18:10 Jesus warns not to despise children because "their angels in heaven always see the face of my Father in heaven." Luke 20:34–36 affirms that, like the angels, "those who are considered worthy of taking part in the age to come and in the resurrection from the dead will neither marry nor be given in marriage, and they can no longer die."

In chapter V of Ignatius of Antioch's Letter to the Trallians, the bishop gives a listing of angels not unlike that later proposed by Pseudo-Dionysius. In his First Epistle of Clement, Clement of Rome exhorts his listeners to join the angels in praising God. Clement of Alexandria wrote that angels "breathe" in men's thoughts and reasonings, and "puts in" their hearts "strength" and a keener perception. Evagrius Ponticus spoke of the concept of angelic companions and angels as models for behavior.

Augustine of Hippo remarks, the angels were experiencing something new as the creation of God unfolded. Augustine also considers that the 'good' angels seek at all times, to direct us towards the true source of happiness, God; that they encourage us in worship of God.

According to Pseudo-Dionysius the Areopagite's De Coelesti Hierarchia (On the Celestial Hierarchy), there are three levels ("sphere") of angels, inside each of which there are three orders.

Various works of Christian theology have devised hierarchies of angelic beings. The most influential Christian angelic hierarchy was put forward around the turn of the 6th century CE by Pseudo-Dionysius in his work De Coelesti Hierarchia. He claimed to be an important figure who was converted by Paul the Apostle, and the Pseudo-Dionysius enjoyed greater influence than he would have if he had used his actual name, until Erasmus publicised doubts about the age of the work in the early 16th century.

According to the Catechism of the Catholic Church (CCC) paragraph 328, "the existence of the spiritual, non-corporeal beings that Sacred Scripture usually calls 'angels' is a truth of faith. The witness of Scripture is as clear as the unanimity of Tradition." The same catechism states: "The whole life of the church benefits from the mysterious and powerful help of the angels [...] From its beginning until death, human life is surrounded by their watchful care and intercession." It also states, "Christ is the center of the angelic world. They are His angels [...] They belong to Him because they were created through and for Him".