This report describes the availability, quantity, quality, variability, and cost of development of the ground-water resources in the Upper Susquehanna River basin in Pennsylvania, which is the entire drainage area in Pennsylvania above the confluence of the West Branch and the main stem of the Susquehanna River at Northumberland. The report has been prepared for and under specifications established by the Corps of Engineers, U. S. Army, and is intended to serve the specific needs for ground-water information for all Federal and State agencies participating in the comprehensive study of the basin.