Sensors transduce physical quantities. Measurements occur over finite regions of space. The size, geometry, and effective dimension of the measurement region have a large effect on the nature of the measurement and also serve as a coarse means of sensor classification. Point sensors measure in a region that is sufficiently small to be approximated as a point. Distributed sensors measure over larger regions with an effective dimension greater than zero. This chapter describes the operating principles and uses of many of the point sensors commonly used for SHM. Chapter 3 covers distributed sensors. The organization of this chapter is somewhat arbitrary with an alignment that follows the underlying operating mechanisms of the sensors, that is, mechanical, electrical, electromagnetic (EM), optical, modern physics, and/or chemical effects.