  Our review covers microscopic foundations of generalized hydrodynamics (GHD).
As one generic approach we develop form factor expansions, for ground states
and generalized Gibbs ensembles (GGE), and compare the so obtained results with
predictions from GHD. One cornerstone of GHD is the GGE averaged microscopic
currents. They can be obtained using form factors. Discussed is also a second,
completely orthogonal approach based on the availability of a self-conserved
current.
