This chapter focuses on the Burmeister's porpoise, which are described from a specimen captured by fishermen at the mouth of La Plata River, Argentina. It belongs to the family Phocoenidae, whose members share the presence of premaxillary eminences in the skull, a reduced posterior extension of the premaxillae not reaching the nasal, and, at least in the living species, small spatulated teeth. The body is stocky with a small, blunt head lacking a beak and proportionally large flippers. The dorsal fin is a diagnostic feature in this species. It is placed far back, triangular in shape, and canted backward, and its leading edge bears a series of 2-4 rows of tubercles ending near the tip of the fin. The tubercles become larger and sharper in older animals. The flukes are medium sized, with rounded tips and an almost straight trailing edge. Throughout its range, Burmeister's porpoise is found mainly in coastal waters, 100-1000 m from shore and 5-25 m deep. Off Argentina, however, some animals have been captured in waters 30-60 m deep and 50 km from shore. Water temperatures during sightings ranged from 4°C to 19.5°C. Sightings and captures are reported in all seasons, although in some areas such as southern Chile there seem to be seasonal movements following prey. Seasonal occurrence has also been reported in the San Jose Gulf in Argentina. © 2009 Copyright © 2009 Elsevier Inc. All rights reserved.