Batak is a collective term used to identify a number of closely related Austronesian ethnic groups predominantly found in North Sumatra and parts of adjacent provinces, Indonesia, who speak the Batak languages. The term always includes the Toba, and often also the Karo, Simalungun, Pakpak, Angkola and Mandailing, and other related ethnic groups with distinct languages and traditional customs (adat).

While the archaeology of southern Sumatra testifies to the existence of Neolithic settlers, it seems that the northern part of Sumatra was settled by agriculturalists at a considerably later stage. Although the Batak are often considered to be isolated peoples due to their location inland, there is evidence that they have been involved in trade with neighbouring kingdoms for a millennium or more.^{[citation needed]}

The Bataks practiced a syncretic religion of Hinduism and ancestor worshipping for thousands of years. The Batak may be mentioned in Zhao Rugua's 13th-century Description of the Barbarous Peoples, which refers to a 'Ba-ta' dependency of Srivijaya. The Suma Oriental, of the 15th century, also refers to the kingdom of Bata, bounded by Pasai and the Aru kingdom.

Based on this evidence, the Batak may have been involved in procuring important commodities such as camphor, benzoin, and other forest products, but also pepper, for trade with China, perhaps from the 8th or 9th centuries and continuing for the next thousand years. Batak men carried the products on their backs for sale at ports.

It has been suggested that the important port of Barus in Tapanuli was populated by Batak people. A Tamil inscription has been found in Barus which is dated to 1088. Contact with Chinese and Tamil traders took place at Kota Cina, a trading town located in what is now northern Medan that was established in the 11th century. It comprised 10,000 people by the 12th century. Tamil remains have been found on key trade routes to the Batak lands.

These trading opportunities may have caused migration of Batak from Pakpak and Toba to the present-day Karo and Simalungun 'frontier' lands, where they were exposed to greater influence from visiting Tamil traders. The migration of Batak to the Angkola-Mandailing lands may have been prompted by 8th-century Srivijayan demand for camphor.

The Karo marga or tribe Sembiring ("black one") is believed to have originated from their ties with Tamil traders. Specific Sembiring sub-marga, namely Brahmana, Colia, Pandia, Depari, Meliala, Muham, Pelawi, and Tekan, are all of Indian origin. Tamil influence on Karo religious practices are also noted, with the pekualuh secondary cremation ritual being specific to the Karo and Dairi people. Moreover, the Pustaka Kembaren, an origin story of the Sembiring Kembaren, suggests linkages with Pagarruyung in the Minangkabau Highlands.

From the 16th century onward, Aceh increased the production of pepper, an important export commodity, in exchange for rice, which grew well in the Batak wetlands. Batak people in different areas cultivated either sawah (wet rice fields) or ladang (dry rice). The Toba Batak, most expert in agriculture, must have migrated to meet demand in new areas. The increasing importance of rice had religious significance, which increased the power of the Batak high priests, who had responsibility for ensuring agricultural success.