Nebuchadnezzar II, also Nebuchadrezzar II, meaning "Nabu, watch over my heir", was the second king of the Neo-Babylonian Empire, ruling from the death of his father Nabopolassar in 605 BC to his own death in 562 BC. Often titled Nebuchadnezzar the Great, he is regarded as the empire's greatest king, famous for his military campaigns in the Levant and their role in Jewish history, and for his construction projects in his capital of Babylon, including the Hanging Gardens of Babylon. Ruling for 43 years, Nebuchadnezzar was the longest-reigning king of the Babylonian dynasty. By the time of his death, he was among the most powerful rulers in the world.

Possibly named after his grandfather of the same name, or after Nebuchadnezzar I (r. c. 1125–1104 BC), one of Babylon's greatest ancient warrior-kings, Nebuchadnezzar II had already secured renown for himself during his father's reign, leading armies in the Medo-Babylonian conquest of the Assyrian Empire. At the Battle of Carchemish in 605 BC, Nebuchadnezzar inflicted a crushing defeat on an Egyptian army led by Pharaoh Necho II, and ensured that the Neo-Babylonian Empire would succeed the Neo-Assyrian Empire as the dominant power in the ancient Near East. Shortly after this victory, Nabopolassar died and Nebuchadnezzar became king.

Despite his successful military career during his father's reign, Nebuchadnezzar's early reign saw few achievements, and witnessed a disastrous failed invasion of Egypt. This performance led some of Babylon's vassals to doubt Babylon's power and was the cause of brewing rebellion across his empire. After first putting down some insurrections in the east, Nebuchadnezzar turned his attention to the Levant and in the 580s BC engaged in a string of campaigns against his rebellious vassal states. In 587 BC, Nebuchadnezzar besieged Jerusalem and destroyed it and the Kingdom of Judah, deporting much of its population in what became known as the Babylonian captivity. This episode earned Nebuchadnezzar a position of notoriety in Jewish history. Through this conquest, the subsequent capture of the Phoenician city of Tyre, and other campaigns in the Levant, Nebuchadnezzar restored the Neo-Babylonian Empire's fortunes in the ancient Near East.

Beyond his military campaigns, Nebuchadnezzar is remembered as a great builder who erected many of Babylon's religious buildings, including the Esagila and Etemenanki, embellished its palaces and beautified its ceremonial centre through renovations to the city's processional street and the Ishtar Gate. He is also accredited with the construction of the Hanging Gardens of Babylon. As most of Nebuchadnezzar's inscriptions deal with his building projects rather than military accomplishments, he was for a time seen by historians mostly as a builder rather than a warrior.

There are few cuneiform sources for the period between 594 BC and 557 BC, which covers much of the reign of Nebuchadnezzar II and the reigns of his three immediate successors, Amel-Marduk, Neriglissar and Labashi-Marduk. This lack of sources has had the unfortunate effect that even though Nebuchadnezzar's reign was the longest among the Neo-Babylonian kings, less is confidently known about it than others. Though the handful of cuneiform sources recovered, notably the Babylonian Chronicle, confirm some events of his reign, such as conflicts with the Kingdom of Judah, other events, such as the 586 BC destruction of Solomon's Temple and other military campaigns Nebuchadnezzar possibly conducted, are not covered in any known cuneiform documents.

As a result, historical reconstructions of this period generally follow secondary sources in Hebrew, Greek and Latin to determine what events transpired at the time, in addition to contract tablets from Babylonia. Though use of the sources written by later authors, many of them created several centuries after Nebuchadnezzar's time and often reflecting their own cultural attitudes to the events and figures discussed, presents problems in and of itself, blurring the line between history and tradition, it is the only possible approach to gain insight into Nebuchadnezzar's reign.

Nebuchadnezzar II's name in Akkadian was Nabû-kudurri-uṣur, meaning "Nabu, watch over my heir". The name was often interpreted in earlier scholarship as "Nabu, protect the boundary", given that the word kudurru can also mean 'boundary' or 'line'. Modern historians support the 'heir' interpretation over the 'boundary' interpretation in terms of this name. There is no reason to believe that the Babylonians intended the name to be difficult to interpret or to have a double meaning.

Nabû-kudurri-uṣur is typically anglicised to 'Nebuchadnezzar', following how the name is most commonly rendered in Hebrew and Greek, particularly in most of the Bible. In Hebrew, the name was rendered as נְבוּכַדְנֶאצַּר (Nəḇūḵaḏneʾṣṣar) and in Greek it was rendered as Ναβουχοδονόσορ (Nabouchodonosor). Some scholars, such as Donald Wiseman, prefer the anglicisation "Nebuchadrezzar", with an "r" rather than an "n", following the assumption that "Nebuchadnezzar" is a later, corrupted form of the contemporary Nabû-kudurri-uṣur.