The Neo-Babylonian Empire or Second Babylonian Empire, historically known as the Chaldean Empire, was the last polity ruled by monarchs native to ancient Mesopotamia. Beginning with the coronation of Nabopolassar as the King of Babylon in 626 BC and being firmly established through the fall of the Assyrian Empire in 612 - 609 BC, the Neo-Babylonian Empire was conquered by the Achaemenid Persian Empire in 539 BC, less than a century after the founding of the Chaldean dynasty. The defeat of the Assyrian Empire and subsequent return of power to Babylon marked the first time that the city, and southern Mesopotamia in general, had risen to dominate the ancient Near East since the collapse of the Old Babylonian Empire (under Hammurabi) nearly a thousand years earlier. The period of Neo-Babylonian rule thus saw unprecedented economic and population growth throughout Babylonia, as well as a renaissance of culture and artwork as Neo-Babylonian kings conducted massive building projects, especially in Babylon itself, bringing back many elements from the previous 2,000 years of Sumero-Akkadian culture.

The Neo-Babylonian Empire retains a notable position in modern cultural memory due to the invidious portrayal of Babylon and its greatest king Nebuchadnezzar II in the Bible. The biblical description of Nebuchadnezzar focuses on his military campaign against the Kingdom of Judah and particularly the Babylonian siege of Jerusalem in 587 BC, which resulted in the destruction of Solomon's Temple and the subsequent Babylonian captivity. Babylonian sources describe Nebuchadnezzar's reign as a golden age that transformed Babylonia into the greatest empire of its time.

Religious policies introduced by the final Babylonian king Nabonidus, who favoured the moon god Sîn over Babylon's patron deity Marduk, eventually served as a casus belli for Persian king Cyrus the Great, who invaded Babylonia in 539 BC by portraying himself as a champion of Marduk divinely restoring order to Mesopotamia. After the conquest, Babylon remained culturally distinct for centuries, with references to people with Babylonian names and to the Babylonian religion known from as late as the Parthian Empire in the 1st century BC. Although Babylon revolted several times during the rule of later empires, it never successfully restored its independence.

Babylonia was founded as an independent state by an Amorite chieftain named Sumu-abum c. 1894 BC. For over a century after its founding, it was a minor and relatively weak state, overshadowed by older and more powerful states such as Isin, Larsa, Assyria and Elam. But Hammurabi (r. c. 1792–1750 BC) turned Babylon into a major power and eventually conquered Mesopotamia and beyond, founding the Old or First Babylonian Empire. After his death, his dynasty lasted another century and a half, but the Babylonian Empire quickly collapsed, and Babylon once more became a small state. Babylonia fell to the Hittite king Mursili I c. 1595 BC, after which the Kassites took control and ruled for almost five centuries before being deposed by native Babylonian rulers, who continued to rule the Babylonian rump state.

The population of Babylonia in this so-called "Post-Kassite" or Middle Babylonian period comprised two main groups, the native Babylonians (composed of the descendants of the Sumerians and Akkadians and the assimilated Amorites and Kassites) and recently arrived, unassimilated tribesmen from the Levant (Suteans, Arameans and Chaldeans). By the 8th century BC, the constituent groups of the native Babylonians, the main population in the large cities, had lost their old identities and had assimilated into a unified "Babylonian" culture. At the same time, the Chaldeans, though retaining their tribal structure and way of life, were becoming more "babylonized", many adopting traditional Babylonian names. These Babylonized Chaldeans became important players in the Babylonian political scene and by 730 BC, all the major Chaldean tribes had produced at least one Babylonian king.

The 9th and 8th centuries BC were catastrophic for the independent Babylonian kingdom, with many weak kings either failing to control all the constituent groups, to defeat rivals, or to maintain important trade routes. This collapse eventually resulted in their powerful northern neighbor, the Neo-Assyrian Empire, conquering and incorporating Babylonia in 729 BC, with the King of Assyria becoming also King of Babylon. The conquest began a century-long struggle for Babylonian independence against an unstable Assyrian rule, including several unsuccessful Babylonian revolts.

Early in the reign of the Neo-Assyrian king Sinsharishkun, the southern official or general Nabopolassar revolted amid ongoing political instability in Assyria, caused by an earlier brief civil war between Sinsharishkun and the general Sin-shumu-lishir. In 626 BC, Nabopolassar assaulted and successfully seized the cities of Babylon and Nippur. Sinsharishkun's response was quick and decisive; by October of that year the Assyrians had recaptured Nippur and besieged Nabopolassar at the city of Uruk. However, Sinsharishkun failed to capture Babylon, and Nabopolassar endured the siege of Uruk, repulsing the Assyrian army.

In November 626 BC, Nabopolassar was crowned King of Babylon, restoring Babylonia as an independent kingdom after more than a century of direct Assyrian rule. The Assyrian king had little success in his campaigns in northern Babylonia from 625 to 623 BC, as Der and other southern cities joined Nabopolassar. Sinsharishkun led a massive counterattack in 623 BC which seemed on a path to victory, but he had to abandon the campaign as a revolt in Assyria threatened his throne at home.