A method of and apparatus for determining the spatial distribution of polarisation properties of an optical fiber (1). Pulses (7) of light are transmitted along the optical fiber (1) and the polarisation state of light backscattered from portions e and elements R of the optical fiber (1) detected. A spatial distribution of linear retardance .delta., orientation of linear retardance axes q and circular retardance axes can be accurately determined. This has application in the analysis of Polarisation Mode Dispension (PMD) in telecommunications as well as, inter alia, strain, stress, temperature and electric current and voltage measurement using optical fibers.