Recent advances in GRB emission theory include application of radiative transfer methods and progress in understanding physics of jets, their dissipative and radiative mechanisms. Fermi GBM and LAT observations have played a special role in these developments. They help to identify the origin of prompt emission and to measure the parameters of blast waves from GRB explosions, their Lorentz factors and ambient densities. The results provide evidence for Wolf-Rayet winds around GRB progenitors. LAT data with simultaneous optical observations also give estimates for magnetic fields in the blast waves. Future discoveries are expected from Fermi observations combined with TeV detections by ground-based Cherenkov detectors, X-ray polarization measurements, and detection of neutrinos. Fermi observatory will continue to play a key role in detecting gamma-ray counterparts of neutron star mergers emitting gravitational waves. It can reveal the details of off-axis emission in short GRBs and thus help reconstruct the explosion picture.