Generalised contact structures are studied from the point of view of reduced generalised complex structures, naturally incorporating non-coorientable structures as non-trivial fibering. The infinitesimal symmetries are described in detail, with a geometric description given in terms of gerbes. As an application of the reduction procedure, generalised coKähler structures are defined in a way which extends the Kähler/coKähler correspondence.1 where H ∈ Ω 3 cl (M ), is given by(for details see [5]). The Leibniz identity for • H (2.5a), gives the Maurer-Cartan identity dH = 0. The Dorfman product, • H , is natural in the sense that it is the derived bracket of d H := d + H∧ (with d the de Rham differential), acting on Γ(Equivalent exact Courant algebroids are classified by [H] ∈ H 3 (M, R), a point first noted by Severa [25]. The equivalence of the exact Courant algebroid under isotropic splittings corresponding to some B ∈ Ω 2 (M ) is closely related to the concepts of symmetries in generalised geometry structures. 2.1. Courant algebroid symmetries. Perhaps the most interesting aspect of generalised geometry is the enhanced symmetry group. The symmetry group of the Lie algebroid, given by the commutator of vector fields on T M , is Diff(M ). Exact Courant algebroids have a symmetry group given by Diff(M ) ⋉ Ω 2 cl (M ) if H = 0. Definition 2.3. A generalised almost complex structure on TM is given by J ∈ End(TM ), satisfying J * = −J and J 2 = −id.A generalised almost complex structure can equivalently be described by a maximal isotropic complex subbundle L ⊂ TM ⊗ C, satisfying L ∩L = {0}, forThere is a local one-to-one correspondence between generalised almost complex structures and conformal classes of complex pure spinors, where a complex pure spinor satisfies the non-degeneracy condition (φ, ϕ) M = 0.A generalised almost complex structure, J , is H-involutive if all sections X of the +i-eigenbundle L J are involutive with respect to • H : X 1 , X 2 ∈ L J ⇒ X 1 • H X 2 ∈ L J . Definition 2.4. A generalised complex structure is an H-involutive generalised almost complex structure.