hyperkahler manifolds are one of the main classes of manifolds appearing in berger’s classification of holonomy groups of riemannian manifolds. it is known that for any non-constant map f from a hyperkahler manifold of dimension 2n, the generic fibers of f are either finite or abelian varieties of dimension n. the latter are lagrangian fibrations. i will discuss some open problems and some results concerning lagrangian fibrations on hyperkahler manifolds.