Occupation of the lowlands by groups of Mayan-language speakers during the Archaic and Formative periods is poorly understood, partly because of a lack of sufficient data. This problem is exacerbated by the fact that early deposits often are discovered at the base of deep test excavations and, as such, yield a “window” to the past that is limited in terms of understanding settlement colonization, growth, and differentiation. The southern portion of the site of K'axob, which is located in northern Belize, contains substantial Middle and Late Formative period construction that is relatively accessible under Classic-period plaza surfaces. The results of seven large-scale excavations conducted in both large and small platform complexes are reported here. A suite of radiocarbon assays and ceramic analysis indicate initial construction at K'axob shortly after 800 b.c. Ceramic complexes presented here are typified by a diversity of Middle Formative pottery types (devoid of jar forms), followed by Late Formative pottery featuring a significant increase in vessel volume and local innovations in surface finish. At K'axob, Middle Formative domiciles were large and well equipped, and they featured a separate ancillary kitchen structure to the west. Around 200 b.c., settlement expanded from a nuclear Middle Formative core, and differentiation in residential construction became apparent. A significant aspect of Formative domestic architecture is the inclusion of human remains, which reveal longitudinal trends in the elaboration of mortuary ritual indicative of ancestor-linked social and economic differentiation.