Climatic changes in the late Pleistocene and early Holocene, which had a great impact on the transgression and regression of the Caspian Sea levels, were simultaneous with Mesolithic and Neolithic settlements around the sea. The frequent changes in the Caspian Sea level have directly and indirectly affected the early settlements of prehistoric societies around the Caspian Sea. The impact of these changes and the reaction of humans is the main subject of this research. Despite the importance of this issue, it has not been studied well related to Caspian Sea research, and it is necessary to explain a model for the response of these communities to climate change. In this paper, with an analytical approach, the subsistence of the communities around the Caspian Sea during the transgressions and regressions of the sea level has been discussed. The Khvalynian (18,000-12,000 BP) and Neo-Caspian (10,600-8,400 BP) transgressions caused marine species to play a significant role in the sustenance of these communities, among other resources. The Mangyshlak (12000-10500 BP) and 8.4k (8400 BP) regressions caused a large distance between the identified sites and the sea shores, and as a result, the use of marine resources in the residents' sustenance decreased; but on the other hand, it caused the formation of rich ecosystems for new animals and plants such as gazelles, goats, and sheep. On the southeastern shores of the Caspian Sea, the beginning of Mesolithic settlements was almost simultaneous with the Khvalynian transgression and the proximity of the coasts to the sites, and these settlements continued until later periods. In the eastern Caspian Sea, settlements appear after the end of the Khvalynian transgression and during the Mangyshlak regression. During this period, the sea was still close to the settlements. While in the west, in the middle of the Khvalynian transgression, settlements were in the Upper Paleolithic, and in the north, there was no settlement until about 10,000 BP. While almost most of the communities in West Asia, at the end of the Pleistocene and Early Holocene, began the domestication and food production; the richness of the regions around the Caspian Sea could easily provide the sustenance needs of its communities and the first domestic species appeared only in the west and north at the Eneolithic period.
