Proton structure at high energy. From HERA towards LHC, LHeC

The world's first ep collider, HERA, has opened up a new insight on the proton structure at high energy. HERA ended its 15-year operation in year 2007. In this manuscript, the results from HERA are introduced, concentrating on the topics related to the proton structure. These are vital inputs to the physics at LHC, the largest proton-proton collider which is about to start operation. In addition, there is an ongoing plan for electron-proton colliding experiments at the LHC (called LHeC). This manuscript also describes what are expected at LHC and LHeC, how the study on the proton structure will go on after the HERA. (author)