The article discusses the physical principles governing the organization of biological membranes, focusing on lipid bilayers and their interactions. It reviews experimental data on lipid and lipid-protein interactions to quantify the physical and thermodynamic principles of membrane structure. The authors highlight the importance of understanding these principles for comprehending the physiological roles of membranes, as structure and function are closely interdependent. They emphasize the need for a quantitative theoretical framework in physics, which is often lacking in biological models. The article also discusses the structural properties of lipid bilayers, including the hydrocarbon and head-group regions, and the thermodynamic principles of aggregation. It explores different aggregation processes, such as immiscible liquids, hydrated ions, lipid aggregates, and spherical micelles. The authors also discuss the structure of multi-component membranes, including mixed-lipid bilayers, proteins in membranes, and local curvature. The article concludes with a discussion of the thermodynamic principles of lipid self-assembly, emphasizing the importance of entropy in self-aggregation and the need for a general theoretical framework to understand the complex organization of membranes.The article discusses the physical principles governing the organization of biological membranes, focusing on lipid bilayers and their interactions. It reviews experimental data on lipid and lipid-protein interactions to quantify the physical and thermodynamic principles of membrane structure. The authors highlight the importance of understanding these principles for comprehending the physiological roles of membranes, as structure and function are closely interdependent. They emphasize the need for a quantitative theoretical framework in physics, which is often lacking in biological models. The article also discusses the structural properties of lipid bilayers, including the hydrocarbon and head-group regions, and the thermodynamic principles of aggregation. It explores different aggregation processes, such as immiscible liquids, hydrated ions, lipid aggregates, and spherical micelles. The authors also discuss the structure of multi-component membranes, including mixed-lipid bilayers, proteins in membranes, and local curvature. The article concludes with a discussion of the thermodynamic principles of lipid self-assembly, emphasizing the importance of entropy in self-aggregation and the need for a general theoretical framework to understand the complex organization of membranes.