The echoes reflected by a sound ping emerging from an active sonar when it interacts with a target in its path can be remotely sensed by a receiver. The presented approach capitalizes on an inverse scattering method that exploits the presence of certain resonance features in the echoes returned by targets to classify them. Classifying underwater objects is important to naval programs such as mine countermeasures (MCM) and anti-submarine warfare (ASW) to preclude wasting of ordnance on false targets. Although the classification of complex shapes is still aformidable task, considerable progress has been made in classifying simple shapes such as spheroidal or cylindrical shells. This methodology has emphasized the extraction, isolation, and labeling of resonance features hidden within the echo, but little has been said yet about how these could be used to classify a target. A couple of simple examples illustrate exactly howthese resonances can be linked to the physical characteristics of the target, allowing for its unambiguous characterization. The procedure, although illustrated with active acoustics (i.e., sonar), can be extended to any active return from any sensor, including radar.