Are we allowed to marry Jewish or Christian women? If we are, is any restriction or qualification stipulated for such ‘mixed’ marriages? Are any Islamic rulings specifically applicable to Shi’ah men and women?

A Muslim man may take a Christian or Jewish woman as a fixed-term wife but, as an obligatory precaution, not as a permanent one. It is not permissible on any basis, for him to marry a girl who has no religion whatever. Allah Almighty tells us in the Qur’an:
…do not hold ties of marriage with unbelieving women. Qur’an 60:10
Most Muslim jurists consider that this ayah includes both Christian and Jewish women.