Sounds produced by Finback Whales Balaenoptera physalus were recorded from a stationary hydrophone in the St. Lawrence Estuary from June to September. The vocalizations consisted of frequencies below 120 Hz; impulsive sounds had frequencies up to 1 kHz. Over 80% of the sounds were downsweeping calls. Frequency variations in the downsweeps were correlated with social context. Constant calls, upsweeps, wavers and a frequency and amplitude modulated call were rare and may be context specific. Vocalization rates varied with the number of animals present and context, but could not be used as a census technique. Comparisons are made with the data from other investigators in both the Northwest Atlantic and the Northeast Pacific. Frequency and time characteristics for Finback downsweeps are summarized and discussed as components important for species recognition.