Surface-sensitive sum-frequency vibrational spectroscopy (SFVS) has grown into a most viable analytical tool to investigate Langmuir monolayer systems. It has been successful in deducing information on many key properties of Langmuir films not obtainable by other techniques. This review gives a survey on the current status of SFVS studies of Langmuir monolayers with emphasis on the structures of both surfactant monolayers and interfacial water under various circumstances. (C) 2012 Elsevier B.V. All rights reserved.