Measurement of the Structure of the Proton at HERA

A combination of the reduced $e^{\pm }p$ cross section, previously measured by H1 and ZEUS, has been performed and leads to well constrained QCD fits of the parton densities in the proton. These results, as well as the high-$Q^2$ neutral current deep inelastic scattering cross sections are presented. First direct measurements of the longitudinal structure function $F_L$ are also reported.