Although Christianity exhibits wide doctrinal variety across its traditions, most denominations share a core set of theological tenets concerning the nature of God, the person of Jesus, and the path to human salvation. As a monotheistic tradition, Christianity affirms the existence of one eternal God who created and sustains the universe.⁷⁸ In mainstream Nicene Christianity, this one God is understood through the doctrine of the Trinity: a single divine essence existing eternally as three distinct, co-equal persons—God the Father, God the Son, and the Holy Spirit.⁹¹⁰ Small minority traditions, often termed nontrinitarian, reject this formulation in favor of alternative views of divine unity.

Christian theology concerning Jesus—known as Christology—holds that God the Son, the eternal Word (or Logos), took on human flesh and nature in the person of Jesus of Nazareth, an event termed the Incarnation.¹¹ According to the Definition of Chalcedon formulated in 451 CE, Christ is one person in two distinct natures, fully divine and fully human, united without confusion, change, division, or separation.¹² The Oriental Orthodox churches instead adhere to Miaphysitism, which holds that divinity and humanity are united in one nature within Christ, while the Church of the East historically emphasized the distinction between his two natures.¹³¹⁴

Soteriology, the study of salvation, addresses how human beings are delivered from sin and its consequences, including spiritual death and separation from God. Western Christian thought, heavily influenced by the fourth- and fifth-century theologian Augustine of Hippo, traditionally emphasizes original sin—an inherited condition of moral corruption resulting from the fall of humanity described in the Book of Genesis.¹⁵ In Catholic teaching, salvation involves initial justification by God's grace received through faith and baptism, followed by an ongoing process of sanctification through love, good works, and participation in the sacraments.¹⁶ Protestant theology, rooted in the sixteenth-century Reformation, generally teaches that justification is granted by God's grace alone through faith alone in Christ's atoning sacrifice, apart from human merit. Eastern Christianity places less emphasis on legal concepts of guilt and justification, framing salvation primarily as theosis (or deification), a transformative process in which believers are united with God and share in divine life through grace.¹⁷

Christian eschatology concerns the ultimate destiny of humanity and the cosmos. Mainstream Christian creeds affirm that Christ ascended into heaven following his resurrection and will return at the end of the age to judge the living and the dead.¹⁸¹⁹ This expectation includes the bodily resurrection of the dead, the renewal of creation, and eternal life in the presence of God for the righteous (heaven), contrasted with eternal separation or punishment for the unrepentant (hell).

The sacred scripture of Christianity is the Bible, an anthology of texts composed over more than a millennium in Biblical Hebrew, Aramaic, and Koine Greek.²⁰²¹ Christians regard the Bible as divinely inspired and authoritative for faith, doctrine, and moral life, though traditions differ on whether scripture is the sole infallible rule of faith (a Protestant principle known as sola scriptura) or whether it functions alongside sacred tradition under the interpretive authority of the church's bishops. The Christian Bible is divided into two main sections: the Old Testament and the New Testament.

The Old Testament corresponds to the Hebrew Bible (Tanakh) of Judaism, chronicling the creation of the world, the history of the Israelites, the Mosaic Law, poetic wisdom literature, and the writings of the prophets.²² Early Christians, operating largely in the Hellenistic world, relied primarily on the Septuagint, an ancient Greek translation of Hebrew scriptures produced in Alexandria.²³ Because the Septuagint contained several texts not included in the later rabbinic Hebrew canon of 24 books, Christian branches developed differing Old Testament canons. Protestant Bibles contain 39 Old Testament books matching the contents of the Hebrew Bible. The Catholic Old Testament comprises 46 books, incorporating seven additional works—such as Tobit, Judith, 1 and 2 Maccabees, Wisdom, and Sirach—termed deuterocanonical by Catholics and apocryphal by Protestants. Eastern Orthodox and Oriental Orthodox canons include these works along with several others, with the Ethiopian Orthodox Tewahedo Church maintaining the largest biblical canon in Christendom.

The New Testament, written in Koine Greek during the first century CE, consists of 27 books accepted across almost all Christian denominations. It opens with four canonical Gospels—Matthew, Mark, Luke, and John—which recount the life, ministry, teachings, death, and resurrection of Jesus. The first three, known as the Synoptic Gospels, share substantial material and structural similarities, whereas the Gospel of John presents a distinct theological reflection on Christ as the incarnate Word. Following the Gospels is the Acts of the Apostles, a historical narrative of the early church's expansion from Jerusalem across the Mediterranean. The remainder of the New Testament contains 21 epistles (letters) written by early leaders—most prominently Paul the Apostle—addressing theology and church governance, concluding with the Book of Revelation, an apocalyptic text attributed to John.²⁴ While core New Testament writings circulated widely by the mid-second century, the formal 27-book canon was consolidated in the fourth century through documents such as the Easter letter of Athanasius of Alexandria in 367 and regional synods in Rome, Hippo (393), and Carthage (397).

Christian religious life centers on corporate worship and individual devotion, including prayer, scriptural reading, and the observance of sacred rites.²⁵ Most denominations gather for communal worship on Sunday, referred to as the Lord's Day in commemoration of Christ's resurrection on the first day of the week.²⁶ A minority of groups, such as Seventh-day Adventists, observe the seventh-day Sabbath on Saturday. In liturgical traditions—including Catholicism, Eastern and Oriental Orthodoxy, Anglicanism, and Lutheranism—services follow prescribed patterns known as liturgies, typically divided into the Liturgy of the Word (scripture readings, psalms, a homily or sermon, and creedal recitation) and the Liturgy of the Eucharist.²⁷²⁸ Many non-liturgical Protestant churches, such as Baptist, Evangelical, and Pentecostal congregations, employ more flexible service structures emphasizing congregational singing, extemporaneous prayer, and extended preaching.²⁹³⁰

Central to Christian practice are sacraments (called sacred mysteries in Eastern traditions), which are outward ritual signs instituted by Christ to convey inward spiritual grace.³¹ The Catholic and Orthodox churches recognize seven sacraments: baptism, confirmation (or chrismation), the Eucharist, penance (reconciliation or confession), anointing of the sick, holy orders, and matrimony. Most Protestant traditions recognize two sacraments—or ordinances, where viewed primarily as symbolic acts of obedience—that Jesus directly commanded in the Gospels: baptism and the Eucharist.

Baptism is the rite of initiation into the Christian church, performed by immersing, pouring, or sprinkling water upon a candidate in the name of the Father, the Son, and the Holy Spirit. While Catholic, Orthodox, and many mainline Protestant churches practice infant baptism, Anabaptist, Baptist, and Pentecostal traditions practice believer's baptism, reserving the rite for individuals old enough to make a conscious profession of faith. The Eucharist, also called Holy Communion, the Mass, the Divine Liturgy, or the Lord's Supper, reenacts the Last Supper shared by Jesus with his disciples before his crucifixion. Views on the consecrated bread and wine vary: Catholics affirm transubstantiation (that the substances become the literal body and blood of Christ while retaining their physical appearances); Orthodox Christians affirm a real, mystical change without defining the philosophical mechanism; Lutherans teach a sacramental union; and Reformed and Baptist traditions view Christ's presence as spiritual or commemorative.

Christian devotion is also structured around a liturgical calendar that marks events in the life of Christ and the saints. The two principal feasts are Christmas, which celebrates the Nativity of Jesus, and Easter (or Pascha), which commemorates his resurrection following the fasting season of Lent and the solemnities of Holy Week, including Good Friday.³² Because Western churches use the Gregorian calendar and most Eastern churches calculate movable feasts using the Julian calendar, the two traditions frequently observe Easter on different dates, though periodic convergences—such as on April 20, 2025—have spurred ongoing ecumenical discussions to establish a permanent unified date.³³

Across two millennia of development, Christianity has diversified into an estimated 50,000 distinct denominations and rites worldwide, up from roughly 2,000 in 1900. Scholars and demographers categorize these bodies into several overarching branches based on historical origins, church governance (polity), and theology.

With more than 2.6 billion followers, Christianity accounts for approximately 32.2 to 32.3 percent of the global population of 8.3 billion. While the religion's share of the world population edged downward during the twentieth century—falling from 34.5 percent in 1900 to 32.0 percent in 2020—demographic analyses by the Center for the Study of Global Christianity at Gordon-Conwell Theological Seminary indicate that the Christian population is growing at an annual rate of 0.95 percent, slightly outpacing the overall global population growth rate of 0.86 percent. Projections estimate that the number of Christians will reach 3 billion before 2050 and approach 3.7 billion by 2075. By comparison, Islam—the world's second-largest religion, with over 2 billion adherents—is growing at roughly 1.57 percent annually, narrowing the numerical gap between the two faiths.⁴³

The defining demographic feature of contemporary Christianity is its dramatic geographic shift from the Global North to the Global South. In 1900, more than 82 percent of the world's Christians resided in Europe and North America, while only 17.6 percent lived in Africa, Asia, Latin America, and Oceania. Nearly 69 percent of all Christians now live in the Global South, a proportion projected to reach 78 percent by 2050.

Africa has become the continent with the largest Christian population, home to nearly 780 million believers and experiencing an annual Christian growth rate of 2.6 percent, driven by high fertility rates and religious conversion in sub-Saharan nations such as Nigeria and the Democratic Republic of the Congo. Latin America remains a major demographic center with over 600 million Christians, where historic Catholic majorities are increasingly accompanied by growing Evangelical and Pentecostal communities, particularly in Brazil. Asia is home to more than 415 million Christians, growing at 1.27 percent annually, with significant populations in the Philippines, China, India, and South Korea.

Conversely, traditionally Christian regions in the Global North and the Middle East are experiencing demographic contraction due to secularization, rising numbers of religiously unaffiliated individuals, and lower birth rates. Europe's Christian population stands at approximately 553 million, declining by 0.41 percent per year, while North America's roughly 275 million Christians are decreasing by 0.16 percent annually, though the United States still holds the largest single national Christian population in the world. In the Middle East and North Africa—the historical birthplace of the faith—emigration, conflict, and persecution have reduced the Christian share of the population from 12.7 percent in 1900 to 4.2 percent.

Throughout its history, Christianity has exerted a profound influence on human society, ethics, education, and culture.⁴⁴ In antiquity and the Middle Ages, Christian concepts of human dignity—rooted in the belief that every person is created in the image of God (imago Dei)—contributed to the curtailment of infanticide and gladiatorial combat, and inspired the creation of the first public hospitals, orphanages, and charitable networks. Monastic scriptoria preserved much of Greco-Roman literature, and the medieval church founded the university system in cities such as Bologna, Paris, and Oxford. In the arts, Christian patronage and theology inspired architectural traditions from Byzantine domes to Gothic cathedrals, masterpieces of Renaissance painting and sculpture, and foundational works of Western music by composers such as Johann Sebastian Bach and George Frideric Handel. In the modern era, Christian theological principles were central to the eighteenth- and nineteenth-century abolitionist movements against the Atlantic slave trade, the twentieth-century American Civil Rights Movement, and the global expansion of literacy through vernacular Bible translation.

At the same time, the history of institutional Christianity has been marked by major controversies, episodes of violence, and critiques from both internal reformers and external secular thinkers.⁴⁵⁴⁶ Critics and historians frequently point to the medieval Crusades, the suppression of perceived heresy through ecclesiastical courts such as the medieval and Spanish Inquisitions (established in 1478), and the sixteenth- and seventeenth-century European wars of religion as instances where religious authority was intertwined with state coercion, torture, and warfare. During the era of European imperialism, missionary activity was often entangled with colonial rule, the suppression of indigenous cultures, and the operation of state-backed residential school systems, while biblical passages were cited by pro-slavery factions to justify chattel slavery prior to abolition. Historical tensions with natural science—most famously the seventeenth-century trial of Galileo Galilei over heliocentrism and nineteenth- and twentieth-century fundamentalist opposition to biological evolution—have also fueled debates over the relationship between faith and reason, though many major denominations view evolutionary science and modern cosmology as compatible with Christian belief.⁴⁷

In the twenty-first century, Christian churches confront complex internal debates and institutional challenges. Revelations of widespread clerical sexual abuse and institutional cover-ups within the Catholic Church, as well as similar misconduct scandals in various Protestant and Orthodox bodies, have caused severe moral crises, legal liabilities, and loss of public trust. Furthermore, denominations remain deeply divided over modern social and bioethical questions, including the ordination of women to the priesthood and episcopate, reproductive issues such as abortion and contraception, and the recognition of same-sex marriage and LGBTQ+ rights—debates that have triggered institutional realignments within Anglican, Methodist, Lutheran, and Reformed communions. Looking outward, Christian leaders—including Pope Leo XIV in his 2026 teachings and the World Council of Churches during the 1,700th anniversary commemorations of the Council of Nicaea—have increasingly focused on addressing secularization, environmental stewardship, economic inequality, the persecution of religious minorities, and the ethical implications of artificial intelligence.⁴⁸⁴⁹⁵⁰