Extracted from Wikipedia http://en.wikipedia.org/wiki/Hymn
The word hymn derives from Greek ὕμνος (hymnos), which means "a song of praise".
In ancient and medieval times, stringed instruments such as the harp, lyre and lute were used with psalms and hymns.
Since there is a lack of musical notation in early writings, the actual musical forms in the early church can only be surmised. During the Middle Ages a rich hymnody developed in the form of Gregorian chant or plainsong. This type was sung in unison, in one of eight church modes, and most often by monastic choirs. While they were written originally in Latin, many have been translated.
Later hymnody in the Western church introduced four-part vocal harmony as the norm, adopting major and minor keys, and came to be led by organ and choir. It shares many elements with classical music.
Some groups of Christians have historically excluded instrumental accompaniment, citing the absence of instruments in worship by the church in the first several centuries of its existence, and adhere to an unaccompanied a cappella congregational singing of hymns.
The Protestant Reformation resulted in two conflicting attitudes to hymns. One approach, the regulative principle of worship, favoured by many Zwinglians, Calvinists and some radical reformers, considered anything that was not directly authorised by the Bible to be a novel and Catholic introduction to worship, which was to be rejected. All hymns that were not direct quotations from the Bible fell into this category. Such hymns were banned, along with any form of instrumental musical accompaniment, and organs were ripped out of churches. Instead of hymns, biblical psalms were chanted, most often without accompaniment, to very basic melodies. This was known as exclusive psalmody.
The other Reformation approach, the normative principle of worship, produced a burst of hymn writing and congregational singing. Martin Luther is notable not only as a reformer, but as the author of many hymns including Ein feste Burg ist unser Gott (A Mighty Fortress Is Our God), which is sung today even by Catholics, and Gelobet seist du, Jesu Christ (Praise be to You, Jesus Christ) for Christmas. Luther and his followers often used their hymns, or chorales, to teach tenets of the faith to worshipers. The first Protestant hymnal was published in Bohemia in 1532 by the Unitas Fratrum. Count Zinzendorf, the Lutheran leader of the Moravian Church in the 18th century wrote some 2,000 hymns. The earlier English writers tended to paraphrase biblical texts, particularly Psalms; Isaac Watts followed this tradition, but is also credited as having written the first English hymn which was not a direct paraphrase of Scripture. Watts (1674–1748), whose father was an Elder of a dissenter congregation, complained at age 16, that when allowed only psalms to sing, the faithful could not even sing about their Lord, Christ Jesus. His father invited him to see what he could do about it; the result was Watts' first hymn, "Behold the glories of the Lamb”.
Relying heavily on Scripture, Watts wrote metered texts based on New Testament passages that brought the Christian faith into the songs of the church. Watts has been called "the father of English hymnody", but Erik Routley sees him more as "the liberator of English hymnody", because his hymns, and hymns like them, moved worshipers beyond singing only Old Testament psalms, inspiring congregations and revitalizing worship.
Three hymns written by Watts are in Hymns Old & New: 6 When I Survey; 238 O Bless The Lord, My Soul; 378 In All My Vast Concerns.
Of a similar era are 95, 247, 263, 304 and 305 by German Gerhard Tersteegen (1691-1764) and 351 by German Lutheran Rev. Paulus Gerhardt (1607-1676).
Even earlier hymns are 13 Jesus the Very Thought of Thee, written by French Catholic Abbot - Bernard of Clairvaux (1091-1153), and 308 The Lord's my Shepherd paraphrase by Calvinist William Whittingham (1524-1579).