Modern view of natural membranes has been updated from the original vision emerged from the Fluid Mosaic Model of Singer and Nicolson published in 1972. One of highlighted feature of the new vision is the acceptance of a high density of proteins mixed with lipids organized as a bilayer forming a continuous hydrophobic/hydrophilic limit that dynamically controls the function of biomembranes in the cell. Langmuir monolayers at the air/water interface is practically the unique technique allowing the study of the surface properties of peptides and proteins and their interaction with lipids in a confined ?crowded? condition similar to the that found in natural biomembranes. Even more, the experimental conditions, as the surface covered proportion of the peptide compared with the lipid one or the degree of surface compactness, are quite controlled at will by the investigator. Using Langmuir monolayer many studies can be performed such us: ability of peptides to absorb to clean air/water interfaces (tensio-active properties), to interact with organized lipid monolayers (penetration), surface stability of spread protein/peptide sample, peptide/lipid lateral miscibility, surface rheology, conformation and secondary structure by PM-IRRAS and lateral topography by using the Brewster Angle Microscopy technique (BAM).
