Structure Function Measurements at HERA

Recent structure function results from the H1 and ZEUS Collaborations are presented. The data cover a wide kinematic range of squared four-momentum transfers Q^2, from 0.2 GeV^2 to 30000 GeV^2, and Bjorken x between 5*10^-6 and 0.65. Data from both experiments have been combined, leading to significantly reduced experimental uncertainties. The combined measurements are analysed using a NLO QCD fit, and a set of parton density functions, HERAPDF1.0, is extracted. New direct measurements of the structure function F_L, making use of dedicated low energy runs of the HERA machine, are also presented.