\indent a generalized complex structure (as introduced by hitchin) consists of a complex structure on the direct sum of the tangent and cotangent bundles of a manifold, satisfying a certain integrability condition. a complex manifold can be regarded as a generalized complex manifold in a canonical way. this leads to an enlarged space of deformations: in addition to deformations as a complex manifold, there are also non-commutative and gerby deformations. \indent symplectic manifolds can also be regarded as generalized complex manifolds. for k3 surfaces, a complex structure can be deformed via generalized complex structures to a symplectic structure. it appears that these deformations connect pairs of fourier-mukai equivalent k3s to pairs of mirror k3s. \indent this talk will be an introduction to generalized complex geometry, leading to a description of the above phenomena.