An overview is provided of the geomagnetic storms and impacts on electric power grids associated with the violent Sun-Earth events of October 2003. During the period from 29 to 31 October 2003, two large geomagnetic storms were observed, as measured by periods of high Kp, Ap, and Dst indices. In fact, these storms had Ap rankings of 6th and 16th all time. This ranking would suggest that the October 2003 storms would be significant with regard to geomagnetically induced currents (GIC) in power grids. However, the resulting geomagnetic storms were much lower in delta B and dB/dt intensity than other historically large geomagnetic storms. A variety of geomagnetic storm processes drove observed GIC. For example, ground observations indicated the presence of large dB/dt pulsations and GIC at North American midlatitude locations on 29 October 2003 that may be due to unusually intense Kelvin-Helmholtz shearing. Sustained disturbance conditions at low-latitude and equatorial latitude locations that are likely linked to ring current intensifications may be the source of sustained GIC at these locations and the cause of large power transformer failures. Comparative evaluations will be provided for the 29–31 October 2003 storms and other important and contemporary storms, such as those observed on 13–14 March 1989, 13–14 July 1982, and 15–16 July 2001. Rather than an index-based evaluation method, the comparative evaluations presented in this paper are based on comparisons of storm morphology. This approach provides a more meaningful comparison of geomagnetic field disturbance dynamics that are important to characterize large GIC threats to power grid infrastructures.