Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in West Asia. Located in the center of the Middle East, it covers the bulk of the Arabian Peninsula and has a land area of about 2,150,000 km² (830,000 sq mi), making it the fifth-largest country in Asia, the largest in the Middle East, and the twelfth-largest in the world. It is bordered by the Red Sea to the west; Jordan, Iraq, and Kuwait to the north; the Persian Gulf, Bahrain, Qatar and the United Arab Emirates to the east; Oman to the southeast; and Yemen to the south. The Gulf of Aqaba in the northwest separates Saudi Arabia from Egypt and Israel. Saudi Arabia is the only country with a coastline along both the Red Sea and the Persian Gulf, and most of its terrain consists of arid desert, lowland, steppe, and mountains. The capital and largest city is Riyadh; other major cities include Jeddah and the two holiest cities in Islam, Mecca and Medina. With a population of almost 32.2 million, Saudi Arabia is the fourth most populous country in the Arab world.

Pre-Islamic Arabia, the territory that constitutes modern-day Saudi Arabia, was the site of several ancient cultures and civilizations; the prehistory of Saudi Arabia shows some of the earliest traces of human activity outside Africa. Islam, the world's second-largest religion, emerged in what is now Saudi Arabia in the early seventh century. Islamic prophet Muhammad united the population of the Arabian Peninsula and created a single Islamic religious polity. Following his death in 632, his followers expanded Muslim rule beyond Arabia, conquering territories in North Africa, Central, South Asia and Iberia within decades. Arab dynasties originating from modern-day Saudi Arabia founded the Rashidun (632–661), Umayyad (661–750), Abbasid (750–1517), and Fatimid (909–1171) caliphates, as well as numerous other Muslim states in Asia, Africa, and Europe.

Saudi Arabia was founded in 1932 by King Abdulaziz (also known as Ibn Saud), who united the regions of Hejaz, Najd, parts of Eastern Arabia (Al-Ahsa) and South Arabia (Asir) into a single state through a series of military and political campaigns beginning in 1901. The country has since been governed as an absolute monarchy under the House of Saud. In its Basic Law, Saudi Arabia defines itself as a sovereign Arab Islamic state with Islam as its official religion and Arabic as its official language. The ultraconservative Wahhabi religious movement within Sunni Islam was the prevailing political and cultural force until the 2000s. The Saudi government has attracted criticism for various policies such as its intervention in the Yemeni Civil War, restrictions on political and civil liberties, and poor human rights record. Since the mid-2010s, Saudi Arabia has instituted limited and gradual reforms to liberalize social, cultural, and religious life.

Saudi Arabia is considered both a regional and middle power. Since petroleum was discovered in the country in 1938, the kingdom has become the world's second-largest oil producer and leading oil exporter, controlling the world's second-largest oil reserves and sixth-largest gas reserves. Saudi Arabia is categorized as a World Bank high-income economy and is the only Arab country among the G20 major economies. The Saudi economy is the largest in the Middle East and the world's nineteenth-largest by nominal GDP and seventeenth-largest by PPP. Ranking very high in the Human Development Index, Saudi Arabia offers free university tuition, no personal income tax, and free universal health care. With its dependence on foreign labour, Saudi Arabia has the world's third-largest immigrant population, with foreign-born residents comprising roughly 40% of the population. Saudi Arabians are among the world's youngest people, with approximately half being under 25 years old. Saudi Arabia is a member of the Gulf Cooperation Council, United Nations, Organisation of Islamic Cooperation, Arab League, and OPEC, as well as a dialogue partner of the Shanghai Cooperation Organisation.

Following the amalgamation of the Kingdom of Hejaz and Nejd, Abdulaziz issued a royal decree on 23 September 1932 naming the new state al-Mamlaka al-ʿArabiyya as-Suʿūdiyya (Arabic المملكة العربية السعودية), which is normally translated as "the Kingdom of Saudi Arabia" in English, but literally means "the Saudi Arab Kingdom", or "the Saudi Kingdom of Arabia" (compare the Hashemite Kingdom of Jordan).

The word "Saudi" is derived from the element as-Suʿūdīyya in the Arabic name of the country, which is a type of adjective known as a nisba, formed from the dynastic name of the Saudi royal family, the Al Saud (Arabic: آل سعود). Its inclusion expresses the view that the country is the personal possession of the royal family. Al Saud is an Arabic name formed by adding the word Al, meaning "family of" or "House of", to the personal name of an ancestor. In the case of Al Saud, this is Saud ibn Muhammad ibn Muqrin, the father of the dynasty's 18th-century founder, Muhammad bin Saud.

There is evidence that human habitation in the Arabian Peninsula dates back to about 125,000 years ago. A 2011 study found that the first modern humans to spread east across Asia left Africa about 75,000 years ago across the Bab-el-Mandeb connecting the Horn of Africa and Arabia. The Arabian Peninsula is regarded as central to the understanding of evolution and dispersals of humanity. Arabia underwent an extreme environmental fluctuation in the Quaternary that led to profound evolutionary and demographic changes. Arabia has a rich Lower Paleolithic record, and the quantity of Oldowan-like sites in the region indicate a significant role that Arabia had played in the early hominin colonization of Eurasia.

In the Neolithic period, prominent cultures such as Al-Magar, whose centre lay in modern-day southwestern Najd, flourished. Al-Magar could be considered a "Neolithic Revolution" in human knowledge and handicraft skills. The culture is characterized as being one of the world's first to involve the widespread domestication of animals, particularly the horse, during the Neolithic period. Al-Magar statues were made from local stone, and it seems that the statues were fixed in a central building that might have had a significant role in the social and religious life of the inhabitants.