South Asia is the southern subregion of Asia, which is defined in both geographical and ethnic-cultural terms. As commonly conceptualised, the modern states of South Asia include Afghanistan, Bangladesh, Bhutan, India, the Maldives, Nepal, Pakistan, and Sri Lanka. However, while Pakistan and Afghanistan are typically categorized as South Asian countries, their cultural, historical, and geopolitical identities are more complex, blending influences from South Asia, Central Asia, and the Middle East. As a result, their classification within South Asia remains a subject of debate.

South Asia borders East Asia to the northeast, Central Asia to the northwest, West Asia to the west and Southeast Asia to the east. Apart from Southeast Asia, Maritime South Asia is the only subregion of Asia that lies partly within the Southern Hemisphere. The British Indian Ocean Territory and two out of 26 atolls of the Maldives in South Asia lie entirely within the Southern Hemisphere. Topographically, it is dominated by the Indian subcontinent and is bounded by the Indian Ocean in the south, and the Himalayas, Karakoram, and Pamir Mountains in the north.

The earliest known settled life in South Asia emerged approximately 9,000 years ago in what is now Pakistan, along the western margins of the Indus River Basin, which gradually evolved into the Indus Valley Civilisation of the third millennium BCE. By 1200 BCE, an archaic form of Sanskrit, an Indo-European language, had diffused into India from the northwest, with the Dravidian languages being supplanted in the northern and western regions. By 400 BCE, stratification and exclusion by caste had emerged within Hinduism, and Buddhism and Jainism had arisen, proclaiming social orders unlinked to heredity.

During the early medieval period, Christianity, Islam, Judaism, and Zoroastrianism arrived in South Asia through trade and conquest. Islam first arrived in South Asia through Arab traders as early as the 7th century, particularly along the coastal regions of Sindh and Balochistan (modern-day Pakistan and southwestern Afghanistan). The first Islamic military expedition occurred in 711 CE, when Muhammad ibn al-Qasim, a general of the Umayyad Caliphate, led the conquest of Sindh (Pakistan), marking the beginning of Islamic rule in the region.

A more extensive wave of Islamic expansion came from Central Asia during the 10th and 11th centuries, led by Mahmud of Ghazni (r. 998–1030 CE). Under Ghaznavid rule, which encompassed modern-day Afghanistan, eastern Iran, and much of Pakistan, the city of Lahore (in present-day Pakistan) emerged as a major political and cultural capital. By the 12th century, the Persianate Tajik dynasty of the Ghurids (c. 879–1215 CE) expanded Islamic rule further into northern India. Their conquests set the stage for the establishment of the Delhi Sultanate in 1206, with Delhi (in modern-day India) as its capital. The Delhi Sultanate remained a major power until its dissolution in 1526, when Babur, a descendant of Timur and Genghis Khan, established the Mughal Empire. The Mughals, yet another Islamic dynasty, ushered in over two centuries of relative peace, leaving a legacy of luminous architecture, exemplified by the Taj Mahal.

Following the decline of the Mughals, the British East India Company started to expand its rule in South Asia, transforming region the into a colonial economy while consolidating its sovereignty. British Crown rule began in 1858. The rights promised to its subjects were granted slowly, but technological changes were introduced, and modern ideas of education and the public life took root. In 1947, the British Indian Empire was partitioned into two independent dominions, a Hindu-majority Dominion of India and a Muslim-majority Dominion of Pakistan, amid large-scale loss of life and an unprecedented migration. The 1971 Bangladesh Liberation War, a Cold War episode resulting in East Pakistan's secession, was the most recent instance of a new nation being formed in the region.

South Asia has a total area of 5.2 million km2 (2 million mi2), which is 10% of the Asian continent. The population of South Asia is estimated to be 2.04 billion or about one-fourth of the world's population, making it both the most populous and the most densely populated geographical region in the world.

In 2022, South Asia had the world's largest populations of Hindus, Muslims, Sikhs, Jains, and Zoroastrians. South Asia alone accounts for 90.47% of Hindus, 95.5% of Sikhs, and 31% of Muslims worldwide, as well as 35 million Christians and 25 million Buddhists.

The South Asian Association for Regional Cooperation (SAARC) is an economic cooperation organisation in the region which was established in 1985 and includes all the nations comprising South Asia.