STRUCTURE FUNCTIONS

Recent progress in the understanding of the nucleon is presented. The unpolarized structure functions are obtained with unprecedented precision from the combined H1 and ZEUS data and are used to extract proton parton distribution functions via NLO QCD fits. The obtained parametrization displays an improved precision, in particular at low Bjorken x, and leads to precise predictions of cross-sections for LHC phenomena. Recent data from proton-antiproton collisions at Tevatron indicate further precise constraints at large Bjorken x. The flavor content of the proton is further studied using final states with charm and beauty in DIS ep and pp collisions. Data from polarized DIS or proton-proton collisions are used to test the spin structure of the proton and to constrain the polarized parton distributions.