Fiber-optic technology, although introduced for use in E&P well and reservoir monitoring only about 15 years ago, has blossomed into a highly reliable set of tools which frequently offer monitoring capability not obtainable with traditional sensors which are either permanently installed or run as logging tools or via other intervention methods.  This presentation will provide an overview of optical sensing techniques and sensors such as distributed temperature sensing (DTS), optical pressure gauges, distributed strain measurement for integrity monitoring and distributed acoustic sensing (DAS).  These monitoring systems are deployed individually or as integrated monitoring systems to measure production and injection profiles, diagnose well and completion integrity problems, monitor matrix and fracture stimulation operations,  and provide indication of key reservoir events such as of water, gas or steam breakthrough in naturally flowing or enhanced recovery wells.  A  brief description of deployment techniques for permanently installed and occasional (intervention) monitoring will illustrate how the different fiber-optic measurement technologies may be implemented in onshore and offshore applications. A case will be made for the application of these in the E&P industry, and examples provided to demonstrate their value.