Uruk, the archeological site known today as Warka, was an ancient city in the Near East or West Asia, located east of the current bed of the Euphrates River, on an ancient, now-dried channel of the river in Muthanna Governorate, Iraq. The site lies 93 kilometers (58 miles) northwest of ancient Ur, 108 kilometers (67 miles) southeast of ancient Nippur, and 24 kilometers (15 miles) northwest of ancient Larsa. It is 30 km (19 mi) east of modern Samawah.

Uruk is the type site for the Uruk period. Uruk played a leading role in the early urbanization of Sumer in the mid-4th millennium BC. By the final phase of the Uruk period around 3100 BC, the city may have had 40,000 residents, with 80,000–90,000 people living in its environs, making it the largest urban area in the world at the time. Gilgamesh, according to the chronology presented in the Sumerian King List (SKL), ruled Uruk in the 27th century BC. After the end of the Early Dynastic period, with the rise of the Akkadian Empire, the city lost its prime importance. It had periods of florescence during the Isin-Larsa period, Neo-Assyrian and Neo-Babylonian periods and throughout the Achaemenid (550–330 BC), Seleucid (312–63 BC) and Parthian (227 BC to AD 224) periods, until it was finally abandoned shortly before or after the Islamic conquest of 633–638.

William Kennett Loftus visited the site of Uruk in 1849, identifying it as "Erech", known as "the second city of Nimrod", and led the first excavations from 1850 to 1854. In myth and literature, Uruk was famous as the capital city of Gilgamesh, hero of the Epic of Gilgamesh. Biblical scholars identify Uruk as the biblical Erech (Genesis 10:10), the second city founded by Nimrod in Shinar.

Uruk (/ˈʊrʊk/) has several spellings in cuneiform; in Sumerian it is 𒀕𒆠 unugᵏⁱ; in Akkadian, 𒌷𒀕 or 𒌷𒀔 Uruk (^URUUNUG). Its names in other languages include: Arabic: وركاء or أوروك, Warkāʾ or Auruk; Classical Syriac: ܐܘܿܪܘܿܟ, ʾÚrūk; Biblical Hebrew: אֶרֶךְ‎ ʾÉreḵ; Ancient Greek: Ὀρχόη, romanized: Orkhóē, Ὀρέχ Orékh, Ὠρύγεια Ōrúgeia.

According to the SKL, Uruk was founded by the king Enmerkar. Though the king-list mentions a father before him, the epic Enmerkar and the Lord of Aratta relates that Enmerkar constructed the House of Heaven (Sumerian: e₂-anna; cuneiform: 𒂍𒀭 E₂.AN) for the goddess Inanna in the Eanna District of Uruk. In the Epic of Gilgamesh, Gilgamesh builds the city wall around Uruk and is king of the city.

Uruk went through several phases of growth, from the Early Uruk period (4000–3500 BC) to the Late Uruk period (3500–3100 BC). The city was formed when two smaller Ubaid settlements developed into the cities of Unug and Kullaba and later merged to become Uruk. The temple complexes at their cores became the Eanna District (Unug) dedicated to Inanna and the "Anu" District of Kullaba.

The Eanna District was composed of several buildings with spaces for workshops, and it was walled off from the city. By contrast, the Anu District was built on a terrace with a temple at the top. It is clear Eanna was dedicated to Inanna from the earliest Uruk period throughout the history of the city. The rest of the city was composed of typical courtyard houses, grouped by profession of the occupants, in districts around Eanna and Anu. Uruk was extremely well penetrated by a canal system that has been described as "Venice in the desert". This canal system flowed throughout the city connecting it with the maritime trade on the ancient Euphrates River as well as the surrounding agricultural belt.

The original city of Uruk was situated southwest of the ancient Euphrates River, now dry. Currently, the site of Warka is northeast of the modern Euphrates river. The change in position was caused by a shift in the Euphrates at some point in history, which, together with salination due to irrigation, may have contributed to the decline of Uruk.