The Bin/Amphiphysin/Rvs167 (BAR) domain superfamily, which includes FCH-BAR (F-BAR) domain proteins are membrane-sculpting proteins. Here the authors combine a range of techniques and show that the F-BAR domain of growth-arrest specific protein 7 (GAS7) forms two-dimensional sheets on flat membranes and that these oligomeric assemblies of GAS7 are required for the formation of phagocytic cups in macrophages.