During 5-7 September 1990, the Scientific Council held a Special Session on "Management Under Uncertainties Related to Biology and Assessments, with Case Studies on Some North Atlantic Fisheries" at the Lord Nelson Hotel, Halifax, Nova Scotia, Canada, with J. Shepherd (EEC-UK) as convener. Keen interest in the contributions and associated discussions prompted the Scientific Council to consider publishing all contributions in a single volume of NAFO Scientific Council Studies. Of the 22 presentations made at the Session, 16 papers and 5 extended abstracts were accepted for publication in this issue of Studies after review by the convener and the editor. The contributions are printed in the order they were presented at the Session.