Everyone who wants to enter the Kingdom of Saudi Arabia has to have a valid passport with at least 6 months validity and the appropriate visa.
Unless you are a visitor from a GCC country or in transit, all other nationalities require a visa to enter the Kingdom.  Visas can be for business, tourist, transit, residency, family, Hajj/Umra, or conference attendance.
Visas can be obtained from the visa department in the Saudi Embassy of the visitor's home country or from Saudi Consulates available in all main cities around the world.
Very recently, it is being approved that all business people are granted the necessary visa at the port of entry.