This paper provides a methodology to extract the dynamic real time model of an electric power system using phasor measurement unit (PMU) data (GPS-synchronized) and other SCADA data that are available in substations. In addition to typical voltage and current measurements, PMU data include frequency and rate of change of frequency. Such data are available in raw form, as time-stamped instantaneous values, or, in the case of voltages and currents, as computed phasor data at the system fundamental frequency. A dynamic state estimator is conceptually presented that filters all available data to extract the transient swings of the system in real time. This means that the power system dynamic state estimator can be essentially used as a real time data processor, and its results can provide filtered input to many power system dynamic monitoring and control applications that are currently unavailable, such as monitoring transient stability.