It is difficult to define the term Contemporary Christian music, but most seem to narrow it down to artists who profess Christ openly, and sing music that is filled with gospel themes.
The roots of Contemporary Christian Music are undeniably from the Jesus movement at the tail-end of the sixties. Many of these followers were former hippies, and so their style of music was influenced by 'secular' sources. By the mid-seventies, Contemporary Christian music had developed into a genre unto its own, usually being sold at Christian bookstores, but very little at major record outlets.
In the eighties, stand-out Christian music artists began to emerge, such as Amy Grant, Michael W. Smith, Carman, and Petra. No longer was Christian music simply rock anymore, but a diversity of genres including rap, alternative, and even heavy metal, which many Christians called 'devil-music'.
In the nineties, many Christian musicians, including Amy Grant, began to do what is called 'mainstreaming'. Since they had proven to 'secular' record companies that they were able to sell their albums, several signed over in order to increase record sales and reach a wider, non-Christian audience. Many Christians criticized such musicians, but it has led to a more diverse spectrum. There are some bands, even though they are not 'Christian bands', still profess to have Christian beliefs, even though their songs are not overtly Christian in theme.
The future will more than likely blur the line between what is Christian and secular music, as more and more genres that one would consider 'secular' are covered by Christian artists. Music countdowns everywhere have included several Christian songs in their playlist, and this trend seems likely to continue.