Bending elasticity is a crucial parameter for our understanding of the
structures and phase sequences in surfactant systems. Theoretical mod
els that stress in particular the interfacial aspect of such systems h
elp us to understand and rationalize these systems of monolayers or bi
layers. Considerable advances have been made, from both a theoretical
and an experimental point of view, in relating the bending moduli to m
olecular parameters of amphiphilic systems. Recent systematic experime
ntal studies have allowed us to obtain a more comprehensive picture of
the dependencies of the bending parameters on the molecular compositi
on of the corresponding surfactant films.