Saudi Arabia is an Islamic State. Islam is the country's established religion, and as such its institutions receive government support. Saudi Arabia is home to the religion's most holiest city, Mecca. Islam started in Saudi Arabia, Allah's final messenger, Muhammad, was born in Mecca.
The vast majority of the fifteen to twenty million Saudis are Salafi Muslims, an orthodox movement within Sunni Islam. Around 15% of citizens are Shia Muslims, most of whom live in the Eastern Province. Saudi Arabia has an estimated foreign population of 8 million, most of whom are Muslim.
The Masjid al-Haram, also known as the Sacred Mosque in Mecca is the largest mosque in the world.