Islam is monotheistic whereas Christianity is triunal.
Both believe in Jesus Christ though he is a prophet in Islam and the son of God in Christianity.
Both are considered to be universal religions which can be accepted by anyone regardless of their race, culture & language.
Both encourage good behaviours and works, service to mankind and to God.
Both believe in the great prophets such as Moses, Abraham, Jacob, Joseph, Noah etc.
Essentially both discourage violence though both religions have had their history of fanaticism.
Christians don't accept Muhammad as a prophet.
Muslims don't consider St. Paul as a saint.
Muslims follow dietry laws similair to the Jews but Christians don't necessarily.
Both are semitic religions meaning they began in the middle east by middle eastern peoples.