Membrane asymmetry refers to the non-equilibrium distribution of lipids and proteins between the two leaflets of plasma membranes, which requires significant free energy. This asymmetry is maintained by lipid translocation proteins such as flippases, floppases, and scramblases. Recent advances in creating asymmetric model membranes have enabled experimental and computational studies to explore the structural and dynamic coupling between leaflets, which can influence membrane bending rigidity and lipid domain formation. Integral membrane proteins also exhibit asymmetric properties, responding to lipid asymmetry and displaying asymmetric topological orientations. Understanding membrane asymmetry is crucial for cellular physiology, as it impacts various physiological processes. However, quantitative insights remain limited due to challenges in creating precise asymmetric membranes. New experimental protocols now allow for the preparation of vesicles with tailored lipid distributions, enabling studies on how leaflet composition affects properties like lateral diffusion and bending elasticity. Integral membrane proteins adapt to lipid asymmetry and may exhibit asymmetric orientations, which can depend on lipid composition. The biogenesis of membrane asymmetry involves the asymmetric insertion of proteins and lipid trafficking from the endoplasmic reticulum to the plasma membrane. Asymmetric membranes have diverse functions, including the selective permeability barrier and transmembrane signaling. Recent studies have shown that membrane asymmetry can influence protein function and membrane properties, such as the mechanical behavior of lipid bilayers. The interplay between leaflets can lead to dynamic coupling, affecting processes like transmembrane signal transduction. Cholesterol distribution is also influenced by membrane asymmetry, with cholesterol tending to reside in the exoplasmic leaflet. Membrane asymmetry can impact protein activity, as seen in the case of the bacterial enzyme OmpLA, where asymmetry modulates phospholipid hydrolysis rates. Membrane-protein topology is also affected by lipid asymmetry, with proteins like LacY exhibiting reversible topological changes in response to lipid composition. The study of asymmetric membranes has revealed important insights into lipid and protein dynamics, but further research is needed to fully understand the mechanisms and implications of membrane asymmetry. Advances in lipid vesicle preparation and membrane protein reconstitution are essential for future studies. The field of membrane asymmetry is rapidly evolving, with significant implications for cellular physiology and potential applications in personalized medicine.Membrane asymmetry refers to the non-equilibrium distribution of lipids and proteins between the two leaflets of plasma membranes, which requires significant free energy. This asymmetry is maintained by lipid translocation proteins such as flippases, floppases, and scramblases. Recent advances in creating asymmetric model membranes have enabled experimental and computational studies to explore the structural and dynamic coupling between leaflets, which can influence membrane bending rigidity and lipid domain formation. Integral membrane proteins also exhibit asymmetric properties, responding to lipid asymmetry and displaying asymmetric topological orientations. Understanding membrane asymmetry is crucial for cellular physiology, as it impacts various physiological processes. However, quantitative insights remain limited due to challenges in creating precise asymmetric membranes. New experimental protocols now allow for the preparation of vesicles with tailored lipid distributions, enabling studies on how leaflet composition affects properties like lateral diffusion and bending elasticity. Integral membrane proteins adapt to lipid asymmetry and may exhibit asymmetric orientations, which can depend on lipid composition. The biogenesis of membrane asymmetry involves the asymmetric insertion of proteins and lipid trafficking from the endoplasmic reticulum to the plasma membrane. Asymmetric membranes have diverse functions, including the selective permeability barrier and transmembrane signaling. Recent studies have shown that membrane asymmetry can influence protein function and membrane properties, such as the mechanical behavior of lipid bilayers. The interplay between leaflets can lead to dynamic coupling, affecting processes like transmembrane signal transduction. Cholesterol distribution is also influenced by membrane asymmetry, with cholesterol tending to reside in the exoplasmic leaflet. Membrane asymmetry can impact protein activity, as seen in the case of the bacterial enzyme OmpLA, where asymmetry modulates phospholipid hydrolysis rates. Membrane-protein topology is also affected by lipid asymmetry, with proteins like LacY exhibiting reversible topological changes in response to lipid composition. The study of asymmetric membranes has revealed important insights into lipid and protein dynamics, but further research is needed to fully understand the mechanisms and implications of membrane asymmetry. Advances in lipid vesicle preparation and membrane protein reconstitution are essential for future studies. The field of membrane asymmetry is rapidly evolving, with significant implications for cellular physiology and potential applications in personalized medicine.