FFPI sensors can be formed based on a variety of structures [1–5]. In this chapter, various technologies are described for the fabrication of FFPI sensors. Generally, the FP cavities can be formed by manually splicing a hollow-core fiber section between SMF and a diaphragm; by splicing photonic crystal fiber (PCF); and by splicing a section of sapphire fiber to SMF. Manual fabrication of FFP sensors is time consuming and labor intensive, and prone to contamination and damage [5]. In recent years, the new demand for novel sensors such as high-temperature strain and pressure sensors and miniature sensors used in tiny spaces is growing continuously. Novel fabrication techniques for fiber-optic sensors are very much in demand to create new functional sensors. Generally, in-line miniature sensors fabricated directly on optical fiber are difficult to be mass produced with good reproducibility due to the miniature size and extreme hardness of the optical fiber. Femtosecond (fs) lasers, focused ion beam (FIB), 157-nm excimer lasers, and chemical etching of doped fibers are good candidates for fabricating microsensors on fibers.