Here we show an example of how ester carbonyl 2D IR provides direct access to environment and dynamics at the lipid-water interface. It is important to emphasize that while 2D IR spectroscopy is not a surface-specific technique, the vibrational reporters are located precisely at the ~1 nm interface between the hydrophobic acyl chain region and bulk-like water beyond the headgroup region, and thus the measurements provide interfacial information. There are multiple avenues for applying 2D IR spectroscopy to understand how headgroup composition and lipid-lipid interactions determine the interfacial environments, contributing to a more complete understanding of membranes, ranging from the effects of headgroup charges or ion localization , to the effects of transmembrane crowding on interfacial water networks .