Christianity is a religion considered monotheistic. The Christian tradition that G-d consists of the Father, the Son (Jesus) and the Holy Spirit is hard to reconcile with monotheism. Christianity grew out of Jewish roots. A basic tenet of Christianity is that Jesus, a Jew, is the Messiah and son of G-d, while Jews believe that the Messiah is still to come.
Christianity has split into many sects. The relationships between Jews and Christians has, like all human relationships between large groups, varied greatly over time and sub-groups.
- Wikipedia's article on Christianity