During the Late Chalcolithic and Early Bronze Age (c. 6500-4000 BP), the Fertile Crescent in Southwest Asia saw the earliest development of cities anywhere in the world. Climate and environmental factors are generally considered to be significant in these changes because in pre-industrial societies they directly relate to food production and security. The emergence of cities also coincides with a decoupling of settlement and climate trends, suggesting urbanism may have enhanced the adaptive capacity of societies to withstand changing climatic conditions. Urban forms followed a variety of different trajectories, with a much more sporadic and episodic history in the dry farming plains of the North and West of the study region compared to the stable build-up in the irrigated South. Although models dealing with urban growth have emphasized the differential access to agrarian resources as a key driver in promoting hierarchical social systems, climate has rarely been explicitly discussed. In contrast, so-called "collapse" events brought about by extreme, but short-lived, climate changes such as droughts have been blamed for declines in urban and rural populations, social complexity, political systems, and entire empires. However, the extent to which these "collapses" are visible in the archeological record, let alone how far they can be attributed to climate changes, is a matter of intense debate. The archeological and historical record, the variegated environmental conditions, and the deep time perspective on complexity available, make the Fertile Crescent an ideal laboratory for assessing causal links between urban formations and climate fluctuations.