Membranes are more mosaic than fluid, according to recent findings. The traditional "fluid mosaic model" has been challenged by new data showing that membranes are patchy, with segregated regions of structure and function, varying lipid thickness and composition, and crowding and ectodomains limiting lipid exposure. Membranes have been neglected by biochemists due to technical challenges, but recent advances in structure and function data are changing this view. The reductionist view of biology, based on the structure–function hypothesis, suggests that membrane structures are selected for specific functions. Membranes are essential for compartmentalization, and their lipid bilayer must be modified by proteins for nutrient uptake and waste disposal. New findings suggest that membranes are not random two-dimensional liquids but have non-random, patchy distributions. This is supported by the observation that most membrane proteins are oligomeric and form strong associations. Lipids also tend to group together, forming lipid–lipid and lipid–protein interactions. The thickness of a membrane is determined by the interaction between lipid and protein, with the lipid distorting to match the protein. Membrane proteins occupy varying areas of the bilayer, and their ectodomains can create steric restrictions. Fluidity must be reconciled with order, as membranes have local patchiness that allows for segregated regions. The new view suggests that membranes have variable patchiness, thickness, and higher protein occupancy than previously thought. This challenges traditional concepts of membrane organization and requires re-evaluation of pure lipid systems in the presence of proteins. The revised model suggests that membranes are more complex and structured than previously believed.Membranes are more mosaic than fluid, according to recent findings. The traditional "fluid mosaic model" has been challenged by new data showing that membranes are patchy, with segregated regions of structure and function, varying lipid thickness and composition, and crowding and ectodomains limiting lipid exposure. Membranes have been neglected by biochemists due to technical challenges, but recent advances in structure and function data are changing this view. The reductionist view of biology, based on the structure–function hypothesis, suggests that membrane structures are selected for specific functions. Membranes are essential for compartmentalization, and their lipid bilayer must be modified by proteins for nutrient uptake and waste disposal. New findings suggest that membranes are not random two-dimensional liquids but have non-random, patchy distributions. This is supported by the observation that most membrane proteins are oligomeric and form strong associations. Lipids also tend to group together, forming lipid–lipid and lipid–protein interactions. The thickness of a membrane is determined by the interaction between lipid and protein, with the lipid distorting to match the protein. Membrane proteins occupy varying areas of the bilayer, and their ectodomains can create steric restrictions. Fluidity must be reconciled with order, as membranes have local patchiness that allows for segregated regions. The new view suggests that membranes have variable patchiness, thickness, and higher protein occupancy than previously thought. This challenges traditional concepts of membrane organization and requires re-evaluation of pure lipid systems in the presence of proteins. The revised model suggests that membranes are more complex and structured than previously believed.