Lagash (/ˈleɪɡæʃ/; cuneiform: 𒉢𒁓𒆷𒆠 LAGAŠ^KI; Sumerian: Lagaš) was an ancient city-state located northwest of the junction of the Euphrates and Tigris rivers and east of Uruk, about 22 kilometres (14 mi) east of the modern town of Al-Shatrah, Iraq. Lagash (modern Al-Hiba in Dhi Qar Governorate) was one of the oldest cities of the Ancient Near East, and the Lagash state incorporated the cities of Lagash, Girsu, Nina. Girsu (modern Telloh), about 25 km (16 mi) northwest of Lagash, was the religious center of the Lagash state, with its main temple, the E-ninnu, dedicated to the god Ningirsu. The ancient site of Nina (Tell Zurghul), around 10 km (6.2 mi) away, marks the southern limit of the state.

Though some Uruk period pottery shards were found in a surface survey, significant occupation at the site of Lagash began early in the 3rd Millennium BC, in the Early Dynastic I period (c. 2900–2600 BC). Surface surveys and excavations show that the peak occupation, with an area of about 500 hectares occurred during the Early Dynastic III period (c. 2500–2334 BC). The later corresponds with what is now called the First Dynasty of Lagash. Lagash then came under the control of the Akkadian Empire for several centuries. With the fall of that empire, Lagash had a period of revival as an independent power during the 2nd Dynasty of Lagash before coming under the control of the 3rd Dynasty of Ur. After the fall of Ur, there was some modest occupation in the Isin-Larsa and Old Babylonian periods. Lagash was then largely deserted until a Seleucid era fortress was built there in the 2nd century BC.

The dynasties of Lagash are not found on the Sumerian King List (SKL) despite being a power in the Early Dynastic period and a major city in the centuries that followed. One tablet, from the later Old Babylonian period and known as The Rulers of Lagash, was described by its translator as "rather fanciful" and is generally considered to be a satirical parody of the SKL. The thirty listed rulers, in the style of the SKL, having improbable reigns, include seven known rulers from the 1st Dynasty of Lagash, including Ur-Nanshe, "Ane-tum", En-entar-zid, Ur-Ningirsu, Ur-Bau, and Gudea.

Little is known of the first two rulers of Lagash. En-hegal is believed to be the first ruler of Lagash. A tablet with his name describes a business transaction, in which a possible King En-hegal buys land. Both his status and date are disputed. He was followed by Lugalshaengur about whom also little is known. Mesilim, who called himself King of Kish though it is uncertain which city he was from, named Lugalshaengur as an "ensi" of Lagash on a mace head.

While many details like the length of reign are not known for the next ruler, Ur-Nanshe, a number of his inscriptions have been found, most at Lagash with one stele at Ur, which along with Umma, he claimed to have conquered in battle. Almost all deal with the construction of temples, one details how he "built the wester[n] channel at the side of Sa[la]/ channel at the side of S[al] (against) the Amorites". He is described as the "son of Gu-NI.DU" (occasionally as "son of Gur:SAR"), and his inscriptions list a number of sons and daughters. Several inscriptions say "He [had the ships of Dil]mun sub[mit] [timber] (to Lagaš) as tribute." His son Akurgal ruled briefly after him.

The next ruler, Eannatum (earlier referred to as "Eannadu"), son of Akurgal and grandson of Ur-Nanshe, turned Lagash into a major power extending throughout large areas of Mesopotamia and to the east as well. In an inscription found at ancient Adab:

"Eannatum, ruler of Lagash, granted strength by Enlil, nourished with special milk by Ninhursag, nominated by Ningirsu, chosen in her heart by Nanshe, son of Akurgal ruler of Lagash, defeated mountainous Elam, defeated Urua, defeated Umma, defeated Ur. At that time, he built a well of fired bricks for Ningirsu in his (Ningirsu’s) broad courtyard. His personal god is Shulultul. Then, Ningirsu loved Eannatum."

Another inscription detail his destruction of "Kiš, Akšak, and Mari at a place named Antasur". He also claimed to have taken the city of Akshak and killed its king, Zuzu. Eannatum took the city of Uru'az on the Persian Gulf, and exacted tribute as far as Mari; however, many of the realms he conquered were often in revolt. During his reign, temples and palaces were repaired or erected at Lagash and elsewhere and canals and reservoirs were excavated. During his reign, Dilmun was a major trading partner.