Optical fibers are now taken for granted as signal transmission media for telecommunication and the Internet. Optical fibers also provide a versatile platform for sensing a host of physical and chemical effects, and parameters of interest. Though optical techniques for measurements were well known for a long time, utility of optical fibers for sensing and measurements has been recognised and widely appreciated only in the last two to three decades. It has indeed become a subject of intense activity over recent times due to a variety of attractive features, notably their immunity to electromagnetic interference, enabling distributed sensing, and remote collection of sensed data for post processing owing to their compatibility to optical fiber telemetry. Fiber optics offers a versatile platform for realizing a multitude of sensors for a variety of application ss in areas as broad as civilian, defence, biomedical, and so on. Functional principles of some of these sensors could be extremely simple, while some sensors could be ultra-sensitive that could yield extremely small magnitudes of certain measurands. This article is an attempt to review the basic principles that underpin this area of research and expose the readers to few such fiber optical sensors by describing their applications.(star)