Gerbes were introduced by Giraud, following ideas of Grothendieck, to deal with non-abelian cohomology in degree 2. In their simplest form, they allow to give geometric representatives of degree 3 integer cohomology classes, in the same way as one can think of principal circle bundles as geometric representatives of degree 2 integer cohomology classes (via their Chern class). In this talk I will report on current joint work with M. Crainic (Utrecht) and D. Martinez-Torres (PUC-Rio) where we describe a symplectic version of gerbes and relate them to quasi-hamiltonian $T^n$-spaces.