Geoscientists play increasingly important roles in international development amidst population growth and concomitant demands on water resources and exposures to natural hazards. This paper demonstrates the value of geoscientists for public good by detailing the range and depth of contributions within a single case study of Dakar, Senegal. This urban agglomeration is home to 3 million residents and represents a major hub of business and migration within West Africa. Its unique geology and locus within the drought-prone western Sahel contribute to specific challenges that have strongly shaped its present cultural and environmental landscape. Sustainable development in Dakar depends in particular on groundwater monitoring, mapping of cliff retreat and landslides, flood studies, coastal erosion studies, and prediction of the local effect of sea-level rise. These critical geoscientific investigations, including fruitful collaborations between Senegalese and foreign geoscientists, are helping to mitigate the environmental effects of previous unplanned growth and to inform policy going forward.