Najd (Arabic: , pronounced [nadd]), or the Nejd, forms the geographic center of Saudi Arabia, accounting for about a third of the country's modern population and, since the Emirate of Diriyah, acting as the base for all unification campaigns by the House of Saud to bring Arabia under a single polity and under the Salafi jurisprudence.

Historic Najd was divided into three modern administrative regions still in use today. The Riyadh region, featuring Wadi Hanifa and the Tuwaiq escarpment, which houses easterly Yamama with the Saudi capital, Riyadh since 1824, and the Sudairi region, which has its capital in Majmaah. The second administrative unit, Al-Qassim, houses the fertile oases and date palm orchards spread out in the region's highlands along Wadi Rummah in central Najd with its capital in Buraidah, the second largest Najdi city, with the region historically contested by the House of Rashid to its north and the House of Saud to its east and south. The third administrative unit is northerly ail, which features the mountains of Jabal Shammar housing the Tayy capital of ail.



The Hejaz (, also US: ; Arabic: ٱلْحِجَاز, romanized: al-Ḥijāz, lit. 'the Barrier', Hejazi pronunciation: [alħɪˈdʒaːz]) is a region in the west of Saudi Arabia. It includes the cities of Mecca, Medina, Jeddah, Tabuk, Yanbu and Taif. It is also known as the "Western Province" in Saudi Arabia. It is bordered in the west by the Red Sea, in the north by Jordan, in the east by the Najd, and in the south by the 'Asir Region. Its largest city is Jeddah, the second largest city in Saudi Arabia, with Mecca and Medina being the fourth and fifth largest cities respectively in the country. The Hejaz is the most cosmopolitan region in the Arabian Peninsula.The Hejaz is significant for being the location of the Islamic holy cities of Mecca and Medina, the first and second holiest sites in Islam, respectively. As the site of the two holiest sites in Islam, the Hejaz has significance in the Arab and Islamic historical and political landscape. The region of Hejaz is the most populated region in Saudi Arabia, Arabic is the predominant language as in the rest of Saudi Arabia, with Hejazi Arabic being the most widely spoken dialect in the region. Hejazis are of ethnically diverse origins.The region, according to Islamic tradition, is the birthplace of the Islamic prophet Muhammad, who was born in Mecca, which is locally considered to have been founded by the Islamic prophets Abraham and Ishmael, and matriarch Hagar. The area became part of his empire through the early Muslim conquests, and it formed part of successive caliphates, first the Rashidun Caliphate, followed by the Umayyad Caliphate, and finally the Abbasid Caliphate. The Ottoman Empire held partial control over the area; after its dissolution, an independent Kingdom of Hejaz existed briefly in 1925 before being conquered by the neighbouring Sultanate of Nejd, creating the Kingdom of Hejaz and Nejd. In September 1932, the Kingdom of Hejaz and Nejd joined the Saudi dominions of Al-Hasa and Qatif, creating the unified Kingdom of Saudi Arabia.