Relativistic jets are ubiquitous in the Universe. They are unique laboratories for studying the physics of magnetized plasmas, particle acceleration, and radiation processes in extreme conditions that can never be achieved with terrestrial experiments. Some of the most powerful astrophysical jets are those emerging from the centers of active galactic nuclei (AGN). Over the past decade, Fermi expanded our gamma-ray view of jets with its long-term monitoring observations and participation to co-ordinated multi-wavelength campaigns of jetted AGN. In this talk, I will review some fundamental, yet unresolved, issues of jet physics in light of Fermi's key findings and discuss future prospects.