Both species of northern right whale (North Atlantic, Eubalaena glacialís and North Pacific, Eubalaena japonica) are critically endangered. The overall distribution of these small, migratory populations is not well known, especially outside of summer. Passive acoustic monitoring is a tool that could provide information on locations of whales. Better distributional information will inform management efforts to reduce anthropogenic mortalities caused by both ship strikes and fisheries interactions. Recent research on passive acoustic monitoring is summarised, focusing on developments relevant to detection and classification of right whale calls. Some outstanding research requirements are outlined, including the need for the development of models to investigate the potential for risk reduction from acoustic data. Buoys capable of fully automatic whale vocalisation detection, classification and transmission to shore are currently under development.</p