The use of distributed and multiplexed fiber-optic sensors in the process monitoring and control environment is described. Recent application development work based on OTDR signal processing techniques is reviewed. Applications investigated include distributed temperature sensing strain sensing humidity sensing chemical sensing and distributed alarm sensing. Multiplexable fiber-optic sensing applications including edge sensing distance sensing vibration and particle sizing based on photon correlation spectroscopy are also described. The principles underlying these measurement techniques are presented and process application examples are provided.