From Wikipedia 

Christian radio is a radio format that focuses on transmitting programming with a Christian message. Many such broadcasters play popular music of Christian influence, though many programs have talk or news programming covering associated topics that can have a political angle to them. Many Christian radio stations are commercial in nature, and select music in a manner intended to increase profitability of advertisers, thereby increasing the value of the station's advertising, and the station's profits. Other Christian radio stations are supported by listeners, or by Christian organizations or institutions.

Christian music radio outlets mirror commercial radio in many ways, and music in a variety of different genres is available. Many stations play primarily gospel music or worship music, while others play all formats of contemporary Christian music including rock and roll, pop, rap, country, and alternative.

Many Christian radio stations have a mission to encourage their listeners in their faith through encouraging music and teaching, and through supporting ministry events within their listening area.

Popular artists on Christian radio include Third Day, Michael W. Smith, Amy Grant, Mercy Me, Steven Curtis Chapman, Relient K, Switchfoot.

Most Christian radio stations as well as programmers are members of the National Religious Broadcasters organization. There are reportedly 1,600 different Christian broadcasting organizations in the United States, ranging from single stations to expansive networks. It is a common practice for religious broadcasters to purchase many small broadcast translators to create large networks that stretch across large regions.

Christian Radio: Not A Niche Anymore   (Arbitron article)