Off-shell superconformal nonlinear sigma-models in three dimensions

We develop superspace techniques to construct general off-shell N ≤ 4 superconformal sigma-models in three space-time dimensions. The most general N = 3 and N = 4 superconformal sigma-models are constructed in terms of N = 2 chiral superfields. Several superspace proofs of the folklore statement that N = 3 supersymmetry implies N = 4 are presented both in the on-shell and off-shell settings. We also elaborate on (super)twistor realisations for (super)manifolds on which the three-dimensional N-extended superconformal groups act transitively and which include Minkowski space as a subspace