The East Slavs are Slavic peoples speaking East Slavic languages. Formerly the main population of the medieval state of Kievan Rus, by the seventeenth century they evolved into the Russian, Ukrainian, and Belarusian peoples.

Relatively little is known about the Eastern Slavs prior to approximately 859 AD, the date from which the account in the Primary Chronicle starts. The reasons are the apparent absence of a written language (Cyrillic script, created about 863 was specifically for Slavic adoption) and the remoteness of East Slavic lands. What little is known comes from archaeological digs, foreign traveller accounts of the Rus land, and linguistic comparative analyses of Slavic languages.

Very few native Rus' documents dating before the 11th century (none ante-dating the 10th century) have been discovered. The earliest major manuscript with information on Rus' history is the Primary Chronicle, written in the late 11th and early 12th centuries. It lists the twelve Slavic tribal unions who, by the 9th century settled between the Baltic Sea and the Black Sea. These tribal unions were Polans, Drevlyans, Dregovichs, Radimichs, Vyatichs, Krivichs, Slovens, Dulebes (later known as Volhynians and Buzhans), White Croats, Severians, Ulichs, Tivertsi.

The early Slavs were a diverse group of tribal societies in Migration period and early medieval Europe (ca. 5th to 10th centuries) whose tribal organizations indirectly created the foundations for today’s Slavic nations (via the Slavic states of the High Middle Ages).

The first mention of the name Slavs dates to the 6th century, by which time the Slavic tribes inhabited a vast area of central-eastern Europe. Over the following two centuries, the Slavs expanded further, towards the Balkans and the Alps in the south and west, and the Volga in the north and east.

From the 9th century, the Slavs were gradually Christianised, and by the 12th century, they formed the population within a number of medieval Christian states, the East Slavs in the Kievan Rus' and Lithuania, the South Slavs in Bulgaria and Serbia, and the West Slavs in Poland and the Holy Roman Empire (Pomerania, Bohemia).

The question of Slavic origins has generated many theories, none of which have been universally accepted. The competing theories on the origin of Slavs used different types of evidence, had different perspectives upon the issues involved, but also were influenced by political factors. When discussing early "Slavs", one is referring to a diverse set of tribal communities who shared a common language and material culture.