Swarup Gadde University of Melbourne Canonical decompositions of groups and 3-manifolds Friday 10th September, 12:05-12:55pm, Carslaw 175. (Joint work with Peter Scott) We discuss the analogues for groups of JSJ-decompositions of Haken 3-manifolds. A key new ingredient is the analogue of regular neighbourhoods in group theory. The analogues of imbeddings and immersions are already known; these correspond to splittings of groups over particular subgroups and almost invariant sets over subgroups.