Electroweak boson (W, Z, ) measurements in Pb+Pb collisions at p sNN = 2:76 TeV and in p+Pb collisions at p sNN = 5:02 TeV are presented with the ATLAS detector at the LHC. In Pb+Pb, electroweak boson yields are shown to be independent of centrality. Di erential measurements in absolute pseudorapidity are used to investigate nuclear e ects to the free-proton parton distribution function (PDF). The distributions lack the experimental precision to unambiguously identify the presence of nuclear modifications. In p+Pb, the Z boson cross section is measured as a function of center-of-mass rapidity y Z and the momentum fraction of the lead-going parton (Bjorken xPb). The distributions are asymmetric and model predictions underestimate the data at large xPb. The overall shape is best described by including nuclear e ects. The di erential cross section is also measured in di erent centrality classes and shows evidence of spatially-dependent nuclear PDFs. The Z boson production yields are measured as a function of the mean number of participants using Glauber and Glauber-Gribov color fluctuation models. Binary scaling of the yields is observed utilizing the standard Glauber model after applying a centrality-bias correction.