The 3rd millennium BC spans the Early to Middle Bronze Age.

It represents a period of time in which imperialism, or the desire to conquer, grew to prominence, in the city states of the Middle East, but also throughout Eurasia, with Indo-European expansion to Anatolia, Europe and Central Asia. The civilization of Ancient Egypt rose to a peak with the Old Kingdom. World population is estimated to have doubled in the course of the millennium, to some 30 million people.

The Bronze Age occurred roughly between 3000 BC and 2500 BC. The previous millennium had seen the emergence of advanced, urbanized civilizations, new bronze metallurgy extending the productivity of agricultural work, and highly developed ways of communication in the form of writing. In the 3rd millennium BC, the growth of these riches, both intellectually and physically, became a source of contention on a political stage, and rulers sought the accumulation of more wealth and more power. Along with this came the first appearances of mega architecture, imperialism, organized absolutism and internal revolution.

In contemporary history, the third millennium is a period of time that commenced on January 1, 2001, and will end on December 31, 3000, of the Gregorian calendar. This is the third period of one thousand years in the Anno Domini.

As this millennium is currently in progress, its first two decades, the past 2000s and the current 2010s, are the subject of the historian's attention. The remaining part of the 21st century and longer-term trends are researched in Futures studies.