The taxamonic order Cetacea is divided commonly into two distinct living suborders: the Mysticeti or baleen whales and the Odontoceti or toothed whales. The baleen whales are represented by several exceptionally large species of approximately 18m (56ft.) or more in length and the toothed whale by one species in this size range (the sperm whale Physeter macrocephalus). These large whales may present strong targets to sonar instruments leading to misclassification as o non-biological target. Also, several smaller, but closely spaced animals may result in a false classification as a single large target. For these reasons, it is helpful to utilize additional sources of information beyond sonar return to determine the likelihood that the target is a whale. Useful supplemental information can be derived in part from knowledge of:

- the distribution and abundance (geographically and seasonally),
- the social aggregations these animals may form,
- their social behaviors,
- their migration pattern,
- their feeding habits.

With such information, an assessment may be made probabilistically that the target or target characteristics represents a whale. In this paper, a review of these types of information is attempted emphasizing the baleen whale. The amount of information available on baleen whales is very large and growing annually. Only a selective account is attempted here.