Arginine is widely used in such applications as protein refolding, solubilization of proteins and small molecules, protein and small molecule formulation, column chromatography and viral inactivation as summarized in this review. What makes arginine effective in these applications is largely based on its ability to suppress protein-protein interactions and protein-surface interactions. The mechanism of these widespread effects of arginine on proteins can be explained at least in part from its unique interactions with the protein surface. Here we describe the modes of the interactions of arginine with model compounds and proteins and also water molecules, and then attempt to explain the mechanism of its effect on proteins by comparing with the interactions that occur between protein and protein denaturants or stabilizers.