Abstract: Fiber optic and vector hydrophones are two major types of hydrophones that are of great importance to underwater acoustics. The chief advantage of the former is that problems related to the integration of traditional underwater acoustic sensing and sonar data transmission can be resolved from an entirely new perspective, thus improving the reliability and possibly decreasing the total cost of manufacture, operation and maintenance of the sonar system. Because of its inherent directivity and unique vector-phase processing, the vector hydrophone possesses potential advantages in the detection of quiet underwater acoustic targets emitting low frequency and ultra-low frequency noise. Engineering applications for both types of hydrophone have gradually emerged from the research laboratory, and will play an active role in the development of future sonar systems. A brief overview is presented of these two state-of-the-art hydrophones from the viewpoint of sonar design, including the basic physics, principle of operation, key techniques, and applications.