The Hydrologic Toolbox is a Windows-based desktop application for analyzing hydrologic time-series data through a graphical and mapping interface. It integrates and enhances the capabilities of the U.S. Geological Survey's Groundwater and Surface-Water Toolboxes, offering standardized methods for hydrologic analysis. Key features include calculating hydrologic-frequency statistics (such as 7Q10 low-flow values), design flows, flow-duration curves, hydrograph separation using multiple established methods, and estimating groundwater recharge from streamflow data. The software also supports retrieval of streamflow and groundwater-level data from the U.S. Geological Survey National Water Information System and generates text reports summarizing analysis results.