Proton structure and its flavor decomposition

In spite of the tremendous progress achieved in establishing the validity of the Standard Model of weak, electromagnetic and strong interactions, there are still many mysteries. In particular, the structure of the proton, whose mass is in 98% generated by strong interactions [1], cannot be calculated from first principles and has to be investigated experimentally. In this lecture, the present status of our knowledge on the parton decomposition of the proton is shortly summarized.