Muslim males are allowed to marry non-Muslim females but Muslim females are only allowed to marry Muslim males. This is often cited as discrimination and one of the symbols of oppression of Muslim females.
1. Muslim males are not allowed to marry any non-Muslim female. Only Christians and Jews (People of the Book) and not any other religion. This is due to the fact that the scriptures held sacred by Christians and Jews do contain large portions of revelation even though the texts have been distorted and changed. Consequently, in honor of the revelation still remaining in these texts, permission was granted to marry their women. However, the condition of chastity is added to the permission mentioned in the Qur’aan. Consequently, only a woman who is either a virgin, divorcee or widow can be married. This means that the common practice of Muslims from the East coming to Europe and America and finding blue eyed blondes in discos for wives is quite illegitimate. Finding chaste females in the West is more difficult than finding the proverbial “needle in the haystack.” By mid teens, virginity is looked at as a fault rather than a virtue.
2. The reason for allowing men and not women is in order to protect the woman’s religion. If a Muslim man requested his Christian wife not to bring alcohol or pork in his house and that she not wear mini-skirts or kiss his friends, she could comply without affecting her religious teachings. However, If a Christian husband requested his Muslim wife to purchase alcohol and serve him pork, to wear mini-skirts and kiss his friends since it is his custom to kiss the wives of his friends. It is natural for a wife to try to please her husband. In the case of the Muslim wife, that could lead to the destruction of her faith.
3. Marriage to non-Muslims is discouraged in situations where Muslims are weak or in the minority in order to safeguard the religion of the children. If a Muslim man marries a non-Muslim woman in the West and their marriage ends in divorce, or the man dies, the courts will award custody of the children to the wife who will likely raise them as non-Muslims. However, if they were married in a Muslim country, the Shareeµah would not give the children to a non-Muslim mother. They would instead be given to either the husband or his relatives in order to insure they receive a Muslim upbringing.
Ref : www.irf.net