The aim of this report is to provide a summary of the present status of the geology of the Olary Domain, Curnamona Province. It gives a comprehensive, referenced description of all known interpretations of Willyama Supergroup basement stratigraphy, igneous rock suites, structure and tectonics, breccias, scope of metamorphism and alteration, and mineral deposits and regolith. The report builds on and adds considerably to the knowledge held in a series of previous descriptions of this complex region, and will be an important aid for explorers. Research into the formation and nature of the Olary Domain continues, with important contributions coming from industry and the universities, as well as from the Geological Survey Branch of PIRSA. The Palaeo-Mesoproterozoic Curnamona Province is a geological entity that extends from central eastern South Australia into western New South Wales. The Province represents a fragment of a Palaeoproterozoic basin in which the Willyama Supergroup was deposited. The present boundaries are aligned with: western - northern Adelaide Geosyncline (Central Flinders Zone). northern - Eromanga Basin (Great Artesian Basin). northeastern - Bancannia Trough and Koonenberry Belt. southeastern - Redan Geophysical Zone. southern - southern Adelaide Geosyncline; Yunta Arm of Nackara Arc. The majority of the Curnamona Province is obscured by younger sedimentary cover, which varies in age from Neoproterozoic to Holocene. The two principal regions of exposure are the Mount Painter and Mount Babbage Inliers in the northwest, and the Willyama Inliers in the south. The latter is somewhat arbitrarily divided into the Olary and Broken Hill areas, of which the former is the subject of this report. From the perspective of the Curnamona Province as a whole, the Olary and Broken Hill areas constitute a geological entity, which is defined by the presence of the Willyama Supergroup. Initially the separation of the Olary and Broken Hill areas was simply by the South Australia - New South Wales border. An early attempt to define the boundary, in geological terms rather than political, saw the Mundi-Mundi Fault being the divider between the Olary and Broken Hill Blocks. Finally, because their margins are not totally structurally controlled, the Olary and Broken Hill Blocks were redefined into the Olary and Broken Hill Domains. In spite of the need for clarification of the exact position of the domain boundaries, the latter terminology will be used hereon. Low-grade Neoproterozoic Burra Group and Umberatana Group meta-sedimentary rocks unconformably overlie, or are faulted against, Palaeoproterozoic rocks in the Olary Domain to the west, south, and to a limited extent, the north. Aeromagnetic and gravity data, regolith studies and drilling results show that the Olary Domain extends to the north for many tens of kilometres under cover along the Benagerie Ridge towards the central, cratonic part of the Curnamona Province; here the deformed Willyama Supergroup appears to be overlain by Mesoproterozoic sediments and volcanics. Data from the Benagerie Ridge imply that the degree of deformation and metamorphism of the Willyama Supergroup is less than that to the south; however there are exceptions. Cover over the Olary Domain on the Benagerie Ridge is mostly Cainozoic, but in places includes Cambrian and Adelaidean rocks. The geomorphology of the Olary Domain is dominated by a number of isolated inliers composed of the volcano-sedimentary Palaeoproterozoic Willyama Supergroup intruded by Mesoproterozoic granites. There is a significant, but lower, volume of mafic extrusives, and sills and dykes, of various ages from Palaeoproterozoic to Neoproterozoic and late Delamerian age. The inliers are separated by corridors of the Neoproterozoic Adelaide Geosyncline sedimentary sequence, and are partly blanketed by Cainozoic sediments and regolith.