HYPOINVERSE2000 determines earthquake locations and magnitudes from seismic network data like first-arrival P and S arrival times, amplitudes and coda durations. The present versions HYPOINVERSE2000 (version 1.2 or 1.3) are in routine use by many networks. Hypoinverse version 1.3 is the standard location program supplied with the Earthworm seismic acquisition and processing system (AQMS) and has thus gotten wide use. Crustal models can be multiple to cover different regions, and either flat layer or flat layer with linear velocity gradients. Version 1.3 also supports negative magnitudes, independent S models, and crustal models from the HYPOELLIPSE program, including layer models, gradient over halfspace models, depths relative to sea level, negative depths above sea level, and use of station elevations. It is Y2000 compatible.