In this talk I will discuss a recent computation of electroweak parton distribution functions (PDFs) for high-energy lepton colliders. The purpose of these PDFs is to re-sum large electroweak logarithms appearing in the collinear emission of initial-state radiation when the typical energy of the hard scattering process is well above the TeV scale. In this regime various effects take place, which are not present in the usual QCD PDFs used at proton colliders. I will then present a few applications of these PDFs for phenomenological studies at multi-TeV Muon Colliders, specifically in relation to the mixed Z-photon PDF and the muon neutrino PDF.