The deposits of the Hadar Formation preserve a continuous record of hominin habitats and environmental change from ca. 3.45 Ma until a regional disconformity at ca. 2.9 Ma. At Hadar, strata below the disconformity are composed of fluvial sands and well-developed claystone paleosols associated with a large-scale meandering river system and several brief lacustrine intervals associated with westward transgressions of the lacustrine depocenter to the east. Detailed analysis of these deposits indicates a strong cyclicity in the fluvial system with regular intercalations of fully lacustrine, lake margin, or ephemeral floodplain lake facies. Following the disconformity, sediment preservation at Hadar is highly localized and represents a major change in depositional facies and character with strata composed primarily of cut-and-fill channel conglomerates and silt-dominated paleosols. A comprehensive tephrostratigraphic analysis of the Hadar Formation volcanics has identified at least 12 distinct vitric tephra preserved above the disconformity at Hadar until ca. 0.78 Ma. Surprisingly few of these tephra correlate to the early archaeology sites in the adjacent Gona region, which reflect the complex paleogeography of these deposits. New radiometric and paleomagnetic age estimates are in general agreement with previously published results, while previously undated tuffs help refine the chronological framework of the formation.Analysis of the Hadar faunal assemblages indicates that a range of habitats were available to Australopithecus afarensis through time and space including open and closed woodlands, gallery forests, edaphic grasslands, and shrublands. Some of the variation observed in these faunal communities can be explained by the spatial distribution of fauna across the landscape, as well as by the depositional environments with which they are associated. Although there is no clear directional trend observed in habitats through time, the faunal assemblages indicate slightly more xeric conditions beginning around 3.2 Ma with a distinct faunal turnover at 3.0 Ma. This shift may be related to changes in global climate patterns, particularly seasonality. Tests of association between A. afarensis and other taxa, as well as the spatial distribution of A. afarensis across the paleolandscape provide little evidence to suggest a habitat preference for the early hominin despite persisting throughout a half million years of environmental and climatic shifts recorded at Hadar.