Modern humans in the form of Cro-Magnons began arriving in the Iberian Peninsula from north of the Pyrenees some 35,000 years ago. The best known artifacts of these prehistoric human settlements are the famous paintings in the Altamira cave of northern Spain, which were likely created about 15,000 BCE.
The historical peoples of the peninsula were the Iberians and the Celts, the former inhabiting the southwest part of the peninsula and along the Mediterranean side through to the northeast, the latter inhabiting the north and northwest part of the peninsula. In the inner part of the peninsula, where both groups were in contact, a mixed, distinctive, culture was present, known as Celtiberian.
The earliest urban culture is believed to be that of the semi-mythical southern city of Tartessos (perhaps pre-1100 BCE). Between about 500 BCE and 300 BCE, the seafaring Phoenicians, and Greeks founded trading colonies along the Mediterranean coast over a period of several centuries. The Carthaginians briefly took control of much of the Mediterranean coast in the course of the Punic Wars until they were eventually defeated and replaced by the Romans starting in 201 BCE. The base Celt and Iberian population remained in various grades of romanization.

Hispania supplied Rome with food, olive oil, wine and metal. The emperors Trajan, Hadrian, Marcus Aurelius and Theodosius I, the philosopher Seneca and the poets Martial, Quintilian and Lucan were born in Hispania.
The collapse of the Western Roman empire did not lead to the same wholesale destruction of Western classical society as happened elsewhere in Europe, although institutions, infrastructure and economy suffered considerable degradation. Spain's present languages, its religion, and the basis of its laws originate from this period. The centuries of uninterrupted Roman rule and settlement left a deep and enduring imprint upon the culture of Spain.
The first Barbarians to invade Hispania arrived in the 5th century, as the Roman empire decayed. The tribes of Goths, Visigoths, Swebians (Suebi), Alans, Asdings and Vandals, arrived in Spain by crossing the Pyrenees mountain range. This led to the establishment of the Swebian Kingdom in Gallaecia, in the northwest, and the Visigothic Kingdom elsewhere. The Visigothic Kingdom eventually encompassed the entire Iberian Peninsula after the Roman Catholic conversion of the Goth monarchs. The horseshoe arch was originally an example of Visigothic art.

In the 8th century, nearly all the Iberian peninsula was quickly conquered (711–718) by mainly Berber Muslims (see Moors) from North Africa. These conquests were part of the expansion of the Islamic Umayyad Empire. They continued northwards until they were defeated in central France at the Battle of Tours, 732. Only three small Christian counties in the mountains of northern Spain managed to cling to their independence; Asturias, Navarra and Aragon which will eventually become kingdoms.
Under Islam, Christians and Jews were recognized as "peoples of the book", and so given dhimmi status. Christians and Jews were free to practice their religion but faced certain discriminations and financial burdens sometimes. Conversion to Islam proceeded at a steadily increasing pace, starting with the aristocracy, as it offered political, social and economic advantages. By the 11th century Muslims were believed to have outnumbered Christians in Al-Andalus.
The Muslim community in Spain was itself diverse and beset by social tensions. The Berber people of North Africa had provided the bulk of the armies and clashed with the Arab leadership from the Middle East. The Berbers soon gave up attempting to settle the harsh lands in the north of the Meseta Central handed to them by the Arab rulers. Over time large Moorish populations became established, especially in the south in the Guadalquivir River valley, and on the Mediterranean coastal plain of Valencia. Towards the end of their rule they became concentrated in the mountainous region of Granada.

The long period of expansion of Spain's Christian kingdoms, beginning in 722 with the Muslim defeat in the Battle of Covadonga and the creation of the Christian Kingdom of Asturias, only eleven years after the Moorish invasion, is called the Reconquista. As early as 739, Muslim forces were driven out of Galicia, which was to host one of medieval Christianity's holiest sites, Santiago de Compostella. Areas in the north became a base for the Christians. The breakup up of Al-Andalus into the competing Taifa kingdoms helped the consolidating Christian kingdoms. The 1085 conquest of the central city of Toledo largely completed the reconquest of the northern half of Spain. As the Reconquista advanced south, mosques and synagogues were converted into churches.
After a revival of Moorish fortunes in the 12th century, the great Moorish strongholds in the south fell to Christian Spain in the 13th century — Córdoba in 1236 and Seville in 1248. This left only the Muslim enclave of Granada as a tributary state in the south, until 1492 when Isabella and Ferdinand captured Granada. That year Spain's large Jewish community was expelled after the decision implemented by the Spanish Inquisition. The same year also marked the discovery of the New World, when Isabella I funded the voyages of Christopher Columbus. After a Muslim uprising triggered by forced conversions and because of the prospect of yet another Islamic invasion, Muslims were expelled in 1502. As Renaissance New Monarchs Isabella and Ferdinand extended the reforms of their predecessors, which included the weakening of the power of the nobility, Gonzalo Fernández de Córdoba fought with French forces in the Italian Wars, revolutionizing warfare. The combined Spanish kingdoms of Castile and Aragon emerged as a European great power.

The unification of the kingdoms of Castile, León, Aragón, and Navarre laid the basis for modern Spain and the Spanish Empire. Spain became Europe's leading power throughout the 16th and first half of the 17th centuries due to the political, social and military adaptations of the 15th and early 16th centuries. This position was reinforced by the rising output of American silver mines from the middle of the 16th century.
In the 16th century, during the long reigns of the first two Spanish Habsburgs (Charles I and Philip II) Spain reached its apogee. The Spanish Empire included much or all of South and Central America, Mexico (New Spain), the south of North America, the Philippines in Eastern Asia, the Iberian peninsula (including the Portuguese empire (from 1580)), southern Italy, Sicily, parts of Germany, Belgium, Luxembourg, and the Netherlands. It was the first empire about which it was said that the sun did not set. It was an Age of Discovery, with daring explorations by sea and by land, the opening up of new trade routes across oceans, conquests and the beginning of European colonialism. Along with the arrival of precious metals, spices, luxuries, and new agricultural plants, the Spanish explorers and others brought back with them knowledge that transformed the European understanding of the world.
Of note during the 16th and 17th centuries was the cultural efflorescence now known as the Spanish Golden Age and the intellectual movement known as the School of Salamanca.
A lingering "decline of Spain" set in during the 17th century. This stagnation involved political, social and economic factors, but a key to it was the strain of ever-expanding military efforts. For a long time, Spain's military efforts were generally successful in defending the scattered Habsburg empire. But these commitments ultimately bankrupted and bled Spain dry during the vast Thirty Years War. By 1640, with forces stretched across Europe, Spain's reverses included the permanent loss of Portugal, thereby losing Brazil and strongholds in Africa and India.

The war with France in 1793 polarized the country in an apparent reaction against the Gallicised elites. Spain made peace with France in 1795, and in 1796, Spain, in support of France, declared war against Britain and Portugal. The disastrous Spanish economic situation (and other factors) forced the abdication of the Spanish king in favour of Napolean's brother, Joseph Bonaparte. This new foreign monarch was regarded with scorn. On May 2, 1808, the people of Madrid took up a nationalist uprising against the French army, known to the Spanish as the War of Independence, and to the English as the Peninsular War. Napoleon was forced to intervene personally, defeating the Spanish army and Anglo-Portuguese forces. However, further military action by Spanish guerrillas and Wellington's Anglo-Portuguese army, combined with Napoleon's disastrous invasion of Russia, led to the ousting of the French from Spain in 1814, and the return of King Ferdinand VII.
The French invasion proved disastrous for Spain's economy, and left a deeply divided country that was prone to political instability for more than a century. The power struggles of the early part of the century led to the loss of all of Spain's colonies in Latin America, with the exception of Cuba and Puerto Rico.

At the end of the 19th century, Spain lost all of its remaining old colonies in the Caribbean and Asia-Pacific regions, including Cuba, Puerto Rico, Philippines, and Guam to the United States after the Spanish-American War of 1898. In 1899 Spain sold its remaining Pacific possessions to Germany.
"The Disaster" of 1898, as the Spanish-American War became known, gave increased impetus to Spain's cultural revival (Generation of '98) in which there was much critical self examination. However, political stability in such a dispersed and variegated land, comprised of strongly differentiated regional identities and deeply held divisions over governmental legitimacy, would elude the country for some decades and was ultimately imposed via dictatorship in 1939.

The 20th century brought little peace; Spain played a minor part in the scramble for Africa, with the colonization of Western Sahara, Spanish Morocco and Equatorial Guinea. A period of dictatorial rule under General Miguel Primo de Rivera (1923–1931) ended with the establishment of the Second Spanish Republic. The Republic offered political autonomy to the Basque Country, Catalonia and Galicia and gave voting rights to women.
The bitterly fought Spanish Civil War (1936-39) ensued. Three years later the Nationalist forces, led by General Francisco Franco, emerged victorious with the support of Germany and Italy. The Republican side was supported by the Soviet Union and Mexico, but it was not supported by the Western powers due to the British-led policy of Non-Intervention. The Spanish Civil War has been called the first battle of the Second World War; under Franco, Spain was neutral in the Second World War though sympathetic to the Axis.

On November 18, 2002, the oil tanker Prestige sank near to the Galician coast, causing a huge oil spill. It has since been regarded as one of the worst environmental disasters in Spanish history.
March 14, 2004 saw the PSOE party elected into government, with Rodríguez Zapatero becoming the new prime minister of Spain. Since the PSOE's election victory, Rodríguez Zapatero's government has withdrawn Spanish troops from Iraq and tackled a series of social issues, including same-sex marriages, gender-violence and divorce. Zapatero also presided over the Spanish Parliament's approval of the new (and controversial) Statute of Autonomy of Catalonia.
Spain has also experienced increasing immigration since the start of the twenty-first century. In 2005, Spain instituted a 3-month amnesty program through which certain hitherto undocumented aliens were granted legal residency.
On March 15, 2006, ETA declared a "cease fire" which ended on December 30, 2006 with a terrorist attack at Madrid Barajas International Airport in which two Ecuatorians died.