Interfacial monolayers used as membrane models have become a practical technique to obtain detailed information about lateral processes taking place in the membrane. These monolayers are particularly useful to study the interactions and parameters governing lateral distribution of lipid and protein species and the association of different molecules with membrane surfaces. In the last few years, these classical models have been complemented by a whole collection of new techniques that are able to provide spatial information on the structure of the interfacial phospholipid-based films at both microscopic and nanoscopic scales. In the present chapter, some detailed protocols are described on how to prepare phospholipid Langmuir films, obtain structural information from their compression isotherms, and study their structure either in situ at the interface or on transfer onto solid supports by applying different microscopy techniques. The use of exogenous fluorescent probes and the extraction of qualitative and quantitative information from epifluorescence microscopy images are particularly addressed.