Fiber optic sensor technology has wide-ranging potential in sensing and measurement and the aim of this paper is to explore the factors that determine this potential. The basic principles of fiber sensing are well established and share much with fiber communications. However, the implementation technologies can be radically different and the market characteristics contrast totally with the communications sector. We explore these issues in the context of applications in structural monitoring, electromagnetic measurements, and environmental sensing. We also present very brief accounts of underlying principles and a short discussion concerning evolving technologies for fiber sensing.