Neutron reflectometry has developed into a powerful method for studying the structure of a wide variety of interfaces involving solids, liquids, and polymers. The basis of the method is described in terms of the kinematic approximation, which allows a direct connection to be made between neutron reflectivity and the structure factor across the interface. The use of isotopic substitution to break down the structure factors into partial structure factors is then described. As an experimental example, the interface between a surfactant solution and air is analysed in detail to show how an analysis in terms of partial structure factors may be used to derive information directly about interfacial structure with minimal reliance on model fitting. A further example of the determination of structure of an adsorbed layer at the solid/liquid is then considered.
