Presentations on "Structure Functions and Parton Densities" working group are summarized. They include results from various global analyses for the parton distribution functions (PDFs) inside the proton and nucleus, and the impact of new experimental data and progress in theoretical calculations, on the extraction of PDFs. Various studies were also presented regarding the constraints on the proton and nuclear PDFs from some specific experimental data from the LHC, HERA, RHIC, and elsewhere.