Eastern South Asia is a subregion of South Asia. It includes the countries of Bangladesh, Bhutan, India (specifically East India and Northeast India), and Nepal. Geographically, it lies between the Eastern Himalayas and the Bay of Bengal. Two of the world's largest rivers, the Ganges and the Brahmaputra, flow into the sea through Eastern South Asia. The region includes the world's highest mountainous terrain and the world's largest delta, and has a climate ranging from alpine and subalpine to subtropical and tropical. Since Nepal, Bhutan, and northeast India are landlocked, the coastlines of Bangladesh and East India serve as the principal gateways to the region.

With more than 441 million inhabitants, Eastern South Asia is home to 6% of the world's population and 25% of South Asia's population. The Bangladesh, Bhutan, India, Nepal Initiative promotes economic integration in the region. The four countries are members of the South Asian Association for Regional Cooperation and the Bay of Bengal Initiative for Multi-Sectoral Technical and Economic Cooperation. Yunnan Province and the Tibet Autonomous Region of the People's Republic of China (PRC) and Myanmar are historically, economically, and culturally interdependent on Eastern South Asia. The Bangladesh–China–India–Myanmar Forum has established an economic corridor in the region.

Eastern South Asia's archaeological heritage includes Lumbini, the birthplace of the Buddha; the ancient universities and monasteries of Nalanda, Vikramshila, Somapura Mahavihara, Jaggadala, Odantapuri and Mainamati; the Ashokan pillars and the Mauryan Empire-era cities of Pataliputra, champa, Vaishali, Balirajpur, Rajgir, Sisupalgarh, Kalinga and Mahasthangarh; and the ruined fort cities of Wari-Bateshwar, Bhitagarh, and Chandraketugarh. The region has an important Buddhist Tourist Circuit. Eastern South Asia hosts a large number of medieval and early modern mosques, including Adina Mosque, the subcontinent's largest medieval mosque, and the Sixty Dome Mosque, and large caravansaries such as Bara Katra and Katra Masjid. It is home to several outstanding examples of medieval and early modern Hindu temple architecture, particularly the Newa architecture of Nepal and the architecture of Bengal.

Eastern South Asia is a cradle of South Asian civilisation. Historical states in the region include those recorded in Indian epics such as the Mahabharata, including ancient Nepal, Vanga, and Pundra; the Greek and Roman recorded kingdom of Gangaridai; major Hindu and Buddhist kingdoms including Kikata, Videha, Vṛji, Magadha, Nanda, Mauryan, Anga, Kalinga, Kamarupa, Samatata, Kanva, Gupta, Pala, Gauda, Sena, Khadga, Candra, Deva, Tripura, and Cooch Behar State. Major Islamic empires in the region included the Delhi and Bengal Sultanates, and the Suri and Mughal Empires (including the important province of Mughal Bengal). A confederation of Muslim and Hindu aristocrats called the Baro-Bhuyan existed in the late 16th and early 17th centuries.

The Bengal Presidency was established in the 18th century by the British Empire, with its headquarters in Fort William, in coastal southwestern Bengal. The British made Bengal the center of their Indian empire, during which Bengal became synonymous with India. Until the mid-19th century, the Bengal Presidency's jurisdiction covered British-controlled territories in north India, northeast India, and Southeast Asia.

The Governor of Bengal was concurrently the Governor General of India for many years. Fort William's surroundings grew into the port city of Calcutta, which was the capital of India until 1911. After the British Indian Empire was established in 1858 following the Indian Rebellion of 1857, the Bengal Renaissance flourished in Calcutta and other Bengali urban centers. The Indian independence movement, including parts of the movement which created Pakistan, had its origins in the Bengal Presidency. The Parliament of Bengal, including the Bengal Legislative Council and the Bengal Legislative Assembly, was the oldest and largest in British India.

The Bengal Presidency had the highest gross domestic product in British India.

Citing administrative improvement and affirmative action for Bengali Muslims and non-Bengali communities in colonial Assam, the British government enacted the first partition of Bengal in 1905. The new province of Eastern Bengal and Assam, with its own Legislative Council, saw more investments in education and infrastructure. The province was a center of the petroleum, tea, and jute industries. Its capital was Dacca, with a summer capital at Shillong. The summer capital enjoyed the highest per capita income in British India. The All India Muslim League was formed in Dacca to safeguard the interests of British Indian Muslims. But the first partition sparked strong protests from elites in Calcutta and sections of the landed gentry, particularly Bengali Hindus. The protests caused a pan-Indian political crisis. In 1912, East Bengal was reunited with West Bengal as Bengal Province while Assam was separated as Assam Province.