  Electron--proton scattering in elastic and highly inelastic region is
reviewed in a unified approach. The importance of parity--violating scattering
due to electro--weak interference in probing the structure of proton is
emphasized. The importance of longitudnal spin--spin asymmetry as well as
parity violating longitudnal asymmetry to extract the structure functions of
proton in both regions are discussed. The recoil polarization of proton in the
elastic scattering is also discussed.
