Beta-arrestins are proteins that regulate GPCR signaling, e.g. by recruiting endocytic components to remove the receptor from the plasma membrane. Our fluorescence microscopy and QCM-D studies suggest beta-arrestins are recruited specifically by phosphoinositide lipids, bind membranes in a concentration-dependent manner, and can induce membrane curvature. In order to determine how membrane composition and protein concentration controls interaction between beta-arrestins and membranes, we need to use neutron reflection to characterize protein binding to supported bilayers. This will be achieved by studying membranes composed to isolate different types of interaction, titrating them with a relevant range of protein concentration, and using appropriate contrast matching. These results will let us identify the mechanism of interaction and critical steps in the function of beta-arrestins.