The observation of gravitational lensing is challenging at high energies
as only the most powerful sources can be detected. At these energies,
the Fermi Gamma-ray Space Telescope has continuously monitored the whole
sky since 2008, detecting photons from the most luminous objects in the
Universe (e.g. blazars and gamma-ray bursts). I will present the lensing
phenomena observed so far with the Fermi satellite, including the first
evidence for strong gravitational lensing in high energy gamma-rays. The
evidence comes from the observation of a gravitational-lens induced echo
in the light curve of the distant blazar PKS 1830-211.
The second phenomenon, called femtolensing, enabled the derivation of limits on the abundance of primordial black holes abundance. Here gamma-ray bursts, with known redshifts, detected by the Fermi Gamma-ray Burst Monitor (GBM) were used to search for the femtolensing effects caused by compact objects.