A practical damage detection scheme to locate and size damage in bridge structures for which only post-damage modal parameters (i.e., frequencies, damping, and mode shapes) are available for few vibration modes is presented. First, a theory of damage localization and severity estimation (which yields information on the location and severity of damage directly from changes in mode shapes) are formulated. Next, a method to identify modal parameters of the baseline (i.e., undamaged state) structure is formulated. Finally, the practicality of the damage detection scheme is demonstrated by locating and sizing damage in a laboratory-tested plate-girder bridge for which only post-damage modal parameters are available for only a single vibration mode.