In three-dimensional anti-de Sitter (AdS) space, there exist several realizations of \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} -extended supersymmetry, which are traditionally labelled by two non-negative integers p ≥ q such that p + q = \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document}. Different choices of p and q, with \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} fixed, prove to lead to different restrictions on the target space geometry of supersymmetric nonlinear σ-models. We classify all possible types of hyperkähler target spaces for the cases \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} = 3 and \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} = 4 by making use of two different realizations for the most general (p, q) supersymmetric σ-models: (i) off-shell formulations in terms of \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} = 3 and \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} = 4 projective supermultiplets; and (ii) on-shell formulations in terms of covariantly chiral scalar superfields in (2,0) AdS superspace. Depending on the type of \documentclass[12pt]{minimal}
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\begin{document}$ \mathcal{N} $\end{document} = 3, 4 AdS supersymmetry, nonlinear σ-models can support one of the following target space geometries: (i) hyperkähler cones; (ii) non-compact hyperkähler manifolds with a U(1) isometry group which acts non-trivially on the two-sphere of complex structures; (iii) arbitrary hyperkähler manifolds including compact ones. The option (iii) is realized only in the case of critical (4,0) AdS supersymmetry.
