In south-central Iraq, a little east of the modern city of al-Diwaniyah.

Isin was an city of lower Mesopotamia, which flourished during the 20th century BC. No kings of Isin are known from the Sumerian period, and the "Dynasty of Isin" refers to Amorite states in lower Mesopotamia that attained independence with the decline of the 3rd dynasty of Ur. The dynasty of Isin ends at ca. 1730 BC

When the Third Dynasty of Ur slowly collapsed in at the end of the third millennium BCE, a power vacuum was left that the larger city-states scrambled to fill. The last king of the Ur Dynasty, Ibbi-Sin, had not the resources nor the organized government needed to expel the aggressive forces that were invading from Elam. One of his governmental officials, Ishbi-Erra, relocated from Ur to Isin, another city in the south of Mesopotamia, and established himself as a ruler there. Although he is not considered part of the Third Dynasty of Ur, Ishbi-Erra did make some attempts at continuing the dynasty, most likely to justify his rule.

Ishbi-Erra had ill luck expanding his kingdom, however, for other city-states in Mesopotamia rose to power also. Eshnunna and Ashur were developing as powerful centers. However, he did have some military luck in defeating the Elamites who had invaded Ur to the point of retreat. This gave the Isin dynasty control over the culturally significant cities of Ur, Uruk, and the spiritual center of Nippur.

For over 100 years, Isin flourished. Remains of large buildings projects, such as temples, have been excavated. Many royal edicts and law-codes from that period have been discovered. The centralized political structure of Ur III was basically continued, with Isin's rulers appointing governors and other local officials to carry out their will in the provinces. Lucrative trade routes to the Arab-Persian gulf remained a crucial source of income for Isin.

The exact events surrounding Isin's rapid disintigration as a kingdom are largely unknown, but some evidence can be pieced together. Documents indicate that access to water sources presented a huge problem for Isin. Isin also endured an internal coup of a sort when a royally appointed governor of the Lagash province, Gungunum, seized the town of Ur. Ur had been the main center of the Gulf trade; thus this move economically crippled Isin. Additionally, Gungunum's two successors (Abisare and Sumu-el (c. 1905 and 1894) both sought to cut Isin off from its canals by rerouting them into Larsa. Somewhere in between, Nippur was also lost. Isin would never recover. Around 1860, an outsider named Enlil-bani seized the throne of Isin, ending the hereditary dynasty established by Ishbi-Erra over 150 years prior.

Although politically and economically weak, Isin maintained its independence from Larsa for at least another forty years, finally succumbing to Larsa's ruler Rim-Sin.