Saudi Arabia occupies about 80% of the Arabian Peninsula, lying between latitudes 16° and 33° N, and longitudes 34° and 56° E. Because the country's southern borders with the United Arab Emirates and Oman are not precisely defined or marked, the exact size of the country remains unknown. The CIA World Factbook's estimate is 2,250,000 km2 (868,730 sq mi) and lists Saudi Arabia as the world's 13th largest state.

Saudi Arabia's geography is dominated by the Arabian Desert and associated semi-desert and shrubland (see satellite image to right). It is, in fact, a number of linked deserts and includes the 647,500 km2 (250,001 sq mi) Rub' al Khali ("Empty Quarter") in the southern part of the country, the world's largest contiguous sand desert. There are virtually no rivers or lakes in the country, but wadis are numerous. The few fertile areas are to be found in the alluvial deposits in wadis, basins, and oases. The main topographical feature is the central plateau which rises abruptly from the Red Sea and gradually descends into the Nejd and toward the Persian Gulf. On the Red Sea coast, there is a narrow coastal plain, known as the Tihamah parallel to which runs an imposing escarpment. The southwest province of Asir is mountainous, and contains the 3,133 m (10,279 ft) Mount Sawda, which is the highest point in the country.

Except for the southwestern province of Asir, Saudi Arabia has a desert climate with extremely high day-time temperatures and a sharp temperature drop at night. Average summer temperatures are around 113 °F (45 °C), but can be as high as 129 °F (54 °C). In the winter the temperature rarely drops below 32 °F (0 °C). In the spring and autumn the heat is temperate, temperatures average around 84 °F (29 °C). Annual rainfall is extremely low. The Asir region differs in that it is influenced by the Indian Ocean monsoons, usually occurring between October and March. An average of 300 mm (12 in) of rainfall occurs during this period, that is about 60% of the annual precipitation.

Animal life includes wolves, hyenas, mongooses, baboons, hares, sand rats, and jerboas. Larger animals such as gazelles, oryx, and leopards were relatively numerous until the 1950s, when hunting from motor vehicles reduced these animals almost to extinction. Birds include falcons (which are caught and trained for hunting), eagles, hawks, vultures, sand grouse and bulbuls. There are several species of snakes, many of which are venomous, and numerous types of lizards. There is a wide variety of marine life in the Persian Gulf. Domesticated animals include camels, sheep, goats, donkeys, and chickens. Reflecting the country's desert conditions, Saudi Arabia's plant life mostly consists of small herbs and shrubs requiring little water. There are a few small areas of grass and trees in southern Asir. The date palm (Phoenix dactylifera) is widespread.

The population of Saudi Arabia as of July 2013 is estimated to be 26,939,583 including 5,576,076 non-nationals In 1950, Saudi Arabia had a population of 3 million. The ethnic composition of Saudi nationals is 50% Arab, 5% Bedouin Arab, 10% Afro Asian and 35% al-Arab al-Ifriqiyah (Egyptian, Sudanese, Libyan. etc.) . Until the 1960s, a majority of the population was nomadic; but presently more than 95% of the population is settled, due to rapid economic and urban growth. As recently as the early 1960s, the Saudi Arabia's slave population was estimated at 300,000. Slavery was officially abolished in 1962.

The CIA Factbook estimated that as of 2013 foreign nationals living in Saudi Arabia made up about 21% of the population. Other sources report differing estimates. Indian: 1.3 million, Pakistani: 900,000, Egyptian: 900,000, Yemeni: 800,000, Bangladeshi: 500,000, Filipino: 500,000, Jordanian/Palestinian: 260,000, Indonesian: 250,000, Sri Lankan: 350,000, Sudanese: 250,000, Syrian: 100,000 and Turkish: 100,000. There are around 100,000 Westerners in Saudi Arabia, most of whom live in compounds or gated communities.

Saudi Arabia expelled 800,000 Yemenis in 1990 and 1991. An estimated 240,000 Palestinians are living in Saudi Arabia. They are not allowed to hold or even apply for Saudi citizenship, because of Arab League instructions barring the Arab states from granting them citizenship; the only other alternative for them is to marry a Saudi national. Palestinians are the sole foreign group that cannot benefit from a 2004 law passed by Saudi Arabia's Council of Ministers, which entitles expatriates of all nationalities who have resided in the kingdom for ten years to apply for citizenship with priority being given to holders of degrees in various scientific fields. The Articles 12.4 and 14.1 of the Executive Regulation of Saudi Citizenship System can be interpreted as requiring applicants to be Muslim.

In a 2011 news story, Arab News reported, "Nearly three million expatriate workers will have to leave the Kingdom in the next few years as the Labor Ministry has put a 20% ceiling on the country's guest workers." The Saudi–Yemen barrier was constructed by Saudi Arabia against an influx of illegal immigrants and against the smuggling of drugs and weapons. In November 2013, Saudi Arabia expelled thousands of illegal Ethiopians from the Kingdom. Various Human Rights entities have criticised Saudi Arabia's handling of the issue.

Saudi Arabia is divided into 13 provinces (manatiq idāriyya, – singular mintaqah idariyya). The provinces are further divided into 118 governorates (Arabic: manatiq idāriyya, منطقةإدارية, ). This number includes the 13 provincial capitals, which have a different status as municipalities (amanah) headed by mayors (amin). The governorates are further sudivided into sub-governorates (marakiz, sing. markaz).

Saudi Arabia's command economy is petroleum-based; roughly 75% of budget revenues and 90% of export earnings come from the oil industry. The oil industry comprises about 45% of Saudi Arabia's nominal gross domestic product, compared with 40% from the private sector (see below). Saudi Arabia officially has about 260 billion barrels (4.1×1010 m3) of oil reserves, comprising about one-fifth of the world's proven total petroleum reserves.

The government is attempting to promote growth in the private sector by privatizing industries such as power and telecommunications. Saudi Arabia announced plans to begin privatizing the electricity companies in 1999, which followed the ongoing privatization of the telecommunications company. Shortages of water and rapid population growth may constrain government efforts to increase self-sufficiency in agricultural products.

In the 1990s, Saudi Arabia experienced a significant contraction of oil revenues combined with a high rate of population growth. Per capita income fell from a high of $11,700 at the height of the oil boom in 1981 to $6,300 in 1998. Increases in oil prices since 2000 have helped boost per capita GDP to $17,000 in 2007 dollars, or about $7,400 adjusted for inflation. Taking into account the impact of the real oil price changes on the Kingdom's real gross domestic income, the real command-basis GDP was computed to be 330.381 billion 1999 USD in 2010.

Oil price increases of 2008–2009 have triggered a second oil boom, pushing Saudi Arabia's budget surplus to $28 billion (110SR billion) in 2005. Tadawul (the Saudi stock market index) finished 2004 with a massive 76.23% to close at 4437.58 points. Market capitalization was up 110.14% from a year earlier to stand at $157.3 billion (589.93SR billion), which makes it the biggest stock market in the Middle East.‏

OPEC (the Organization of Petroleum Exporting Countries) limits its members' oil production based on their "proven reserves." Saudi Arabia's published reserves have shown little change since 1980, with the main exception being an increase of about 100 billion barrels (1.6×1010 m3) between 1987 and 1988. Matthew Simmons has suggested that Saudi Arabia is greatly exaggerating its reserves and may soon show production declines (see peak oil).

Saudi Arabia is one of only a few fast-growing countries in the world with a relatively high per capita income of $24,200 (2010). Saudi Arabia will be launching six "economic cities" (e.g. King Abdullah Economic City) which are planned to be completed by 2020. These six new industrialized cities are intended to diversify the economy of Saudi Arabia, and are expected to increase the per capita income. The King of Saudi Arabia has announced that the per capita income is forecast to rise from $15,000 in 2006 to $33,500 in 2020. The cities will be spread around Saudi Arabia to promote diversification for each region and their economy, and the cities are projected to contribute $150 billion to the GDP.

However the urban areas of Riyadh and Jeddah are expected to contribute $287 billion by the year 2020.

Gold mining is carried out in the Mahd adh Dhahab region (also known as the "Cradle of Gold"). Saudi Arabian stores suffered a significant decrease in gold sales in 2012.

Reporting of poverty remains a state taboo. In December 2011, days after the Arab Spring uprisings, the Saudi interior ministry detained reporter Feros Boqna and two colleagues and held them for almost two weeks for questioning after they uploaded a video on the topic to YouTube. Statistics on the issue are not available through the UN resources because the Saudi government does not issue poverty figures. Observers researching the issue prefer to stay anonymous because of the risk of being arrested. Three journalists: Feras Boqna, Hussam al-Drewesh and Khaled al-Rasheed were detained after posting 10-minute film 'Mal3ob 3alena', or 'We are being cheated' on Saudis living in poverty to YouTube. Authors of the video claim that 22% of Saudis are considered to be poor (2009) and 70% of Saudis do not own their houses.

Saudi Arabia has centuries-old attitudes and traditions, often derived from Arab tribal civilization. This culture has been bolstered by the austerely puritanical Wahhabi form of Islam, which arose in the eighteenth century and now predominates in the country. The many limitations on behaviour and dress are strictly enforced both legally and socially. Alcoholic beverages are prohibited, for example, and there is no theatre or public exhibition of films. However, the Daily Mail and Wikileaks indicate that the Saudi Royal family applies a different moral code to itself ("WikiLeaks cables: Saudi princes throw parties boasting drink, drugs and sex. Royals flout puritanical laws to throw parties for young elite while religious police are forced to turn a blind eye.") Public expression of opinion about domestic political or social matters is discouraged. There are no organizations such as political parties or labour unions to provide public forums.

Daily life is dominated by Islamic observance. Five times each day, Muslims are called to prayer from the minarets of mosques scattered throughout the country. Because Friday is the holiest day for Muslims, the weekend was Thursday and Friday. Starting on 29 June 2013 the weekend has been shifted to Friday-Saturday to better serve the Saudi economy and its international commitments. In accordance with Wahhabi doctrine, only two religious holidays are publicly recognized, ʿĪd al-Fiṭr and ʿĪd al-Aḍḥā. Celebration of other Islamic holidays, such as the Prophet's birthday and ʿĀshūrāʾ (an important holiday for Shīʿites), are tolerated only when celebrated locally and on a small scale. Public observance of non-Islamic religious holidays is prohibited, with the exception of 23 September, which commemorates the unification of the kingdom.