The 11th century is the period from 1001 (MI) through 1100 (MC) in accordance with the Julian calendar, and the 1st century of the 2nd millennium.

In the history of Europe, this period is considered the early part of the High Middle Ages. There was, after a brief ascendancy, a sudden decline of Byzantine power and a rise of Norman domination over much of Europe, along with the prominent role in Europe of notably influential popes. Christendom experienced a formal schism in this century which had been developing over previous centuries between the Latin West and Byzantine East, causing a split in its two largest denominations to this day: Roman Catholicism and Eastern Orthodoxy.

In Song dynasty China and the classical Islamic world, this century marked the high point for both classical Chinese civilization, science and technology, and classical Islamic science, philosophy, technology and literature. Rival political factions at the Song dynasty court created strife amongst the leading statesmen and ministers of the empire. In Korea, the Goryeo Kingdom flourished and faced external threats from the Liao dynasty (Manchuria).

In this century the Turkish Seljuk dynasty comes to power in Western Asia over the now fragmented Abbasid realm, while the first of the Crusades were waged towards the close of the century. The Fatimid Caliphate in Egypt, the Ghaznavids, and the Chola dynasty in India had reached their zenith in military might and international influence. The Western Chalukya Empire (the Chola's rival) also rose to power by the end of the century. In Japan, the Fujiwara clan continued to dominate the affairs of state.

In the Americas, the Toltec and Mixtec civilizations flourished in Central America, along with the Huari Culture of South America and the Mississippian culture of North America. The Tiwanaku Empire centered around Lake Titicaca collapsed in the first half of the century.