Physics Accomplishments of HERA.

The electron-proton collider HERA at DESY in Hamburg, Germany, delivered luminosity from 1992 to 2007. The center-of-mass energy was a factor of ten higher compared to previous lepton-nucleon scattering experiments. The research at HERA emphasized precision analyses of the proton structure at small x and high Q2. In addition, precision tests of QCD provided significant new insights into the strong force. Diffractive scattering plays an important role in hard interactions. Many searches for new physics were performed at the electron-proton energy frontier. Additionally, two fixed-target experiments that used only the electron and proton beams of HERA, respectively, studied the spin structure of the nucleon and the production of strangeness, charm, and bottom in high-energy proton collisions. This review summarizes key results obtained by the four experiments at HERA: H1, ZEUS, HERMES, and HERA-B. [ABSTRACT FROM AUTHOR]