The Early Agricultural period (EAP) has been a central focus of study in the American Southwest and northwestern Mexico for the past 30 years. This long interval, also considered as part of the Late Archaic in the greater region, comprises the introduction of maize agriculture and the development of sedentary agricultural communities over the course of more than 2000 years. Radiocarbon ages on maize indicate that maize was regularly cultivated by 2100 cal BC in the Tucson Basin; several recently dated specimens from the site of Las Capas suggest maize may have been grown here even earlier, between 2500 to 3700 cal BC. The shift from a mobile hunter-forager economy to a subsistence economy built around maize agriculture was long, and did not follow the trajectory of other agricultural societies world-wide; the Neolithic Demographic Transition in the Southwest was a slow process, prefaced by some 2500 years of agriculture, and did not occur simultaneously across the region. This dissertation comprises three articles that address the EAP in in southern Arizona. The first presents a review of the current status of research on the Archaic in the Tucson Basin, with a focus on the EAP and the past 30 years of work by both academic and Cultural Resource Management institutions. The second article places the EAP and development of agricultural communities in the context of Network Theory and Cultural Niche Construction theory; although regional populations were small, communities throughout northwestern Mexico and the Southwest US were connected by social and economic ties that facilitated the transmission of goods, information, and people, all of which were fundamental to the spread of agriculture and its associated societal consequences. The third article presents a chronological analysis of EAP sites in the Tucson Basin. OxCal is used to model the ages of 12 sites that date to the Silverbell interval and San Pedro phase; 160 radiocarbon ages, most obtained from carbonized maize, are used in the analysis. Temporal variation among sites and their locations along the Santa Cruz River floodplain are evaluated in light of changes in river geomorphology and the cumulative effects of community investment in agricultural infrastructure.