This paper presents an overview of the geology of the wider Hunter Valley and Central Coast regions of New South Wales and a discussion of some of the consequences that present challenges to the geotechnical engineering profession. The contrasting structural styles of the folded and faulted Southern New England Fold Belt and the relatively flat-lying, undeformed Sydney Basin are described and compared. Consideration is given to the potential for instability arising from the combination of competent, blocky conglomerates, low strength claystones and coal seams, particularly within the Newcastle Coal Measures. Of the wide variety of challenges that arise from such a regionally diverse range of geological conditions, three areas of practice are given special discussion due to their local importance. These are the treatment of Quaternary sediments that underlie many of the more intensely developed areas; the distribution, properties and treatment of reactive clay soils that are well developed in all geological environments and the treatment of problems due to the risk of mining-induced subsidence on development.