HERA the new frontier

The large storage ring Hardon-Electron-Ring Accelerator (HERA) has been completed at DESY. The first collisions for physics studies are scheduled for spring 1992. HERA is the first electron-proton storage ring ever built. Electrons and protons of nominal energies, Ee = 30 GeV and Ep = 820 GeV will collide at center of mass energy 314 GeV. The beam energies can be varied, while maintaining luminosity, over the range Ee = 10-35 GeV and Ep = 300-1000 GeV. The theoretical motivations and questions raised by quantum chromodynamics in this new demain are approached at a phenomenological level. The measurement of x the momentum fraction carried by the struck quark inside the proton, and Q2, are reviewed over the accessible domain at HERA energies from the scattered electron and hadron flow laboratory variables. The various experimental methods to extract the gluon distribution are described. Other physics opportunities to test the standard model are briefly given. Finally, a few examples of processes not expected by the standard model, but within the reach of HERA energetics, are outlined