The BAR (Bin/Amphiphysin/Rvs) domain is a highly conserved feature in amphiphysins, endophilins, and nadrins, found across various organisms from yeast to humans. The structure of the Drosophila amphiphysin BAR domain is a crescent-shaped dimer that binds preferentially to highly curved negatively charged membranes. The N-terminal amphipathic helix and BAR domain (N-BAR) can drive membrane curvature both in vitro and in vivo. The structure is similar to arfaptin2, which also binds and tubulates membranes. This suggests that BAR domains are a universal and minimal module for dimerization, membrane binding, and curvature sensing. The N-BAR domain is essential for the formation and stability of the muscle T-tubule network in Drosophila and is involved in synaptic vesicle endocytosis in mammals. Mutations in the basic residues of the N-BAR domain reduce its ability to bind to and tubulate liposomes. The BAR domain is also found in other proteins, such as sorting nexins, centaurins, and oligophrenins, and is often combined with GEF and GAP domains to regulate small GTPases. The BAR domain's ability to sense curvature suggests a role in the spatial and temporal compartmentalization of proteins to specific membrane domains.The BAR (Bin/Amphiphysin/Rvs) domain is a highly conserved feature in amphiphysins, endophilins, and nadrins, found across various organisms from yeast to humans. The structure of the Drosophila amphiphysin BAR domain is a crescent-shaped dimer that binds preferentially to highly curved negatively charged membranes. The N-terminal amphipathic helix and BAR domain (N-BAR) can drive membrane curvature both in vitro and in vivo. The structure is similar to arfaptin2, which also binds and tubulates membranes. This suggests that BAR domains are a universal and minimal module for dimerization, membrane binding, and curvature sensing. The N-BAR domain is essential for the formation and stability of the muscle T-tubule network in Drosophila and is involved in synaptic vesicle endocytosis in mammals. Mutations in the basic residues of the N-BAR domain reduce its ability to bind to and tubulate liposomes. The BAR domain is also found in other proteins, such as sorting nexins, centaurins, and oligophrenins, and is often combined with GEF and GAP domains to regulate small GTPases. The BAR domain's ability to sense curvature suggests a role in the spatial and temporal compartmentalization of proteins to specific membrane domains.