This chapter explores the geological, hydrogeological, geophysical, contamination, and socio-economic aspects of groundwater resources in Nigeria, highlighting the challenges and opportunities related to their exploration, exploitation, and management. Nigeria’s groundwater resources are predominantly sourced from two major hydrogeological terrains—the basement complex covering around 50% of the nation’s landmass and sedimentary terrain spanning the other 50%. The basement complex hosts aquifers within weathered and fractured crystalline hard rock formations, including regolith/overburden aquifers, fractured basement aquifers, and deeper fracture zones. While generally low-yielding with limited storage capacity, localized high groundwater yields can be obtained from highly fractured or deeply weathered zones. In contrast, the sedimentary terrain features are more productive multi-layered and discontinuous aquifer systems within the basins like Chad, Sokoto, Benue Trough, Anambra, Dahomey, and Niger Delta basins, and characterized by higher yields and larger storage potentials. The aquifers within these basins are explored and exploited using a wide range of techniques, including geological, hydrogeological, hydrogeophysical, remote sensing, and geographic information system tools. However, rampant over-exploitation and consequent depletion affect aquifers across both terrains. Recent climate change issues pose a significant threat to groundwater development in Nigeria, impacting groundwater quality and availability. Other challenges include groundwater pollution from industrial, domestic, agricultural and urban activities and an acute lack of comprehensive management policies and regulatory frameworks. Sustainable development necessitates a robust approach involving broad hydrogeological investigations for proper aquifer mapping and characterization, continuous monitoring programs, promotion of managed extraction balanced with artificial recharge initiatives, strategic water distribution infrastructure, and robust policies for water resource protection and equitable utilization. With its sizeable groundwater reserves, Nigeria is positioned to derive substantial socio-economic benefits via an integrated strategy combining technical interventions with institutional strengthening for optimal, judicious, and widespread access to this precious resource across various sectors and communities.