The majority religion in Saudi Arabia is Islam. Islam is the official religion of Saudi Arabia, and all citizens are legally accepted to be Muslims. The government does not legally protect the freedom of religion. As a matter of fact, any overseas national must convert to Islam, should he or she intend acquiring Saudi nationality.  There are many news reports which criticize the Saudi government for its harsh implementation of Islamic rule, its double standards and its poor Human Rights record.
The official form of Islam is Sunni of the Hanbali school, in its Salafi version. Nearly 85-90% of the population are SunniMuslims. Two holiest cities of Islam, Makkah and Medina, are in Saudi Arabia. For many reasons, non-Muslims are not permitted to enter the holy cities, although there are reports of certain Westerners who disguised themselves as devout Muslims and were able to enter.