Recent developments in the application of Raman spectroscopy to carbon–nanotube–based composite materials are reviewed. This technique may be used to identify carbon nanotubes, access their dispersion in polymers, evaluate nanotube/matrix interactions and detect polymer phase transitions. The Raman spectra of nanotubes can also be used to quantify the strain or stress transferred to nanotubes from the surrounding environment and to investigate local stresses and strains in polymers and composites. A polarized Raman technique was developed to detect the stress or strain in a matrix using randomly dispersed single–walled nanotubes. This technique has been used to detect and map stress fields in model fibre–polymer composites. The stress distributions around fibre breaks were mapped and compared with classical load transfer models.