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Canonical extensions were first studied, in the context of Boolean algebras with operators (BAOs), in the classic work of B. Jónsson and A. Tarski [12]. The de-velopment of a corresponding theory in a less restricted setting than that of BAOs lagged far behind. However major advances have been made in the past ten years by M. Gehrke in collaboration with B. Jónsson, J. Harding, Y. Venema and others; see in particular [8], [9] and [10]. Appropriate definitions have been found for canonical extensions of distributive lattice expansions (that is, bounded distributive lattices with additional operations, henceforth called DLEs) and more generally of lattice and even poset expansions. Such structures arise naturally as semantic models of non-classical logics. A variety of algebras is canonical if it is closed under the for-mation of canonical extensions. When the members of a variety are the algebraic models of a logic, canonicity leads inter alia to completeness results for the associ-ated logic (see [7] for selected examples and also [10]). The work of Gehrke et al. has brought many new insights and has revealed symbiotic relationships between duality and canonical extensions. This is resulting in a unification of the hithert