  The Large Area Telescope (LAT) on-board the Fermi satellite detected emission
above 20 MeV only in a small fraction of the long gamma-ray bursts (GRBs)
detected by the Fermi Gamma-ray Burst Monitor (GBM) at 8 keV-40 MeV. Those
bursts that were detected by the LAT were among the brightest GBM bursts. The
emission detected by LAT seerms to be delayed respect to the one detected by
the GBM. In this review I will show the main implications of these LAT
observations on the GRB models and discuss the importance of a synergy between
Fermi and other telescopes.
