A hymn is a religious song of worship in Christianity, or a sacred song. Collections of hymns are known as hymnals. Hymns are often sung by the entire group at church. Sometimes they are sung only by a special group called a choir. A piano or organ often plays the music while people sing. Most hymns are written in four-part harmony. They also often use a common meter. Thus, they tend to have a traditional sound. 
Many early hymns were taken from the Psalms. Later hymns began to include ideas from other parts of the Bible. Isaac Watts and Charles Wesley wrote many hymns. In in more modern times, Fanny Crosby wrote many more. Some hymns are prayers to God. Others tell about God. Songs which describe God or how people relate to Him are also called "gospel songs" instead of hymns.
One of the most famous hymns is Amazing Grace which also became a popular song. It was written by John Newton who was an evil person who later became a Christian. The hymn tells how God saved him from sin even though he was unworthy.  This is an example of God's grace.
- Eskew; McElrath (1980). Sing with Understanding, An Introduction to Christian Hymnology. Broadman Press. ISBN 0-8054-6809-9.
- "Amazing Grace How Sweet the Sound", Dictionary of American Hymnology. Retrieved 31 October 2009.