Beta-arrestins are proteins thought to turn off GPCR receptor signaling by assisting the recruitment of clathrin leading to endocytosis of GPCRs, where the receptor is removed from the plasma membrane and the activating extracellular ligands. Our recent fluorescence microscopy and QCM-D studies suggest beta-arrestins are recruited specifically by phosphoinositide lipids, but that adsorption also is affected by strong non-specific binding. In order to determine how specific and non-specific binding contributes to interaction between beta-arrestins and membranes, we need to use neutron reflection to monitor and characterize protein binding to supported lipid bilayers. This will be achieved by studying a set of membranes composed to isolate different types of interaction, titrating them with a relevant range of protein concentration, and using appropriate contrast matching. The results here obtained will permit us to identify the mechanism of interaction of beta-arrestins with lipid bilayers and thus identify the critical steps in the biological function of this protein.