A hymn is a type of song, and partially synonymous with devotional song, specifically written for the purpose of adoration or prayer, and typically addressed to a deity or deities, or to a prominent figure or personification. The word hymn derives from Greek ὕμνος (hymnos), which means "a song of praise". A writer of hymns is known as a hymnist. The singing or composition of hymns is called hymnody. Collections of hymns are known as hymnals or hymn books. Hymns may or may not include instrumental accompaniment. Polyhymnia is the Greco/Roman goddess of hymns.

Although most familiar to speakers of English in the context of Christianity, hymns are also a fixture of other world religions, especially on the Indian subcontinent (stotras). Hymns also survive from antiquity, especially from Egyptian and Greek cultures. Some of the oldest surviving examples of notated music are hymns with Greek texts.

Ancient Eastern hymns include the Sumerian Kesh temple hymn (oldest surviving literary text in the world); Egyptian Great Hymn to the Aten, composed by Pharaoh Akhenaten; the Hurrian Hymn to Nikkal; the Rigveda, an Indian collection of Vedic hymns; hymns from the Classic of Poetry (Shijing), a collection of Chinese poems from 11th to 7th centuries BC; the Gathas—Avestan hymns believed to have been composed by Zoroaster; and the Biblical Book of Psalms.

The Western tradition of hymnody begins with the Homeric Hymns, a collection of ancient Greek hymns, the oldest of which were written in the 7th century BC, praising deities of the ancient Greek religions. Surviving from the 3rd century BC is a collection of six literary hymns (Ὕμνοι) by the Alexandrian poet Callimachus. The Orphic Hymns are a collection of 87 short poems in Greek religion.

Patristic writers began applying the term ὕμνος, or hymnus in Latin, to Christian songs of praise, and frequently used the word as a synonym for "psalm".

Originally modelled on (but distinct from) the Book of Psalms and other poetic passages (commonly referred to as "canticles") in the Scriptures,^{[citation needed]} Christian hymns are generally directed as praise to the Christian God. Many refer to Jesus Christ either directly or indirectly.

In the New Testament, Saint Paul wrote to the Ephesian and Colossian churches, enjoining the singing of psalms and hymns for "mutual encouragement and edification". This was demonstrated when he joined Silas in singing hymns in the Phillipian jail, even during unfortunate circumstances. Psalms 30:4 and Revelation 14:3, among other Scriptural verses, encourage Christians to sing hymns to praise God. As such, since the earliest times, Christians have sung "psalms and hymns and spiritual songs", both in private devotions and in corporate worship. Non-scriptural hymns (i.e. not psalms or canticles) from the Early Church still sung today include 'Phos Hilaron', 'Sub tuum praesidium', and 'Te Deum'.

The hymn 'Te Deum' is sung or recited in the Liturgy of the Hours and in thanksgiving to God for a special blessing (such as the election of a pope, the consecration of a bishop, the canonization of a saint), and on December 31st to thank the Lord for the past year.