The spontaneous formation of multilayer structures at interfaces from surfactant self-assembly has until recently been rarely observed. However, surface multilayer structures are now emerging as an important and more common structural signature associated with a wide range of technological applications and biological function. Neutron reflectivity, NR, has proved to be an ideal probe of such interfacial structures, and is responsible for the raised awareness of their existence and potential. This proposal is part of a major new programme (supported by EPSRC, EP/G065705) to characterise such structures and to determine the major factor with control their formation, in surfactant mixtures and in polymer / surfactant mixtures. We request here beam time on INTER / SURF to pursue the formation of multilayer structures at the air-solution interface in surfactant and mixed surfactant systems