Optical fibers are neither intrinsically sensitive nor selective; hence, it can be difficult to design a fiber-optic hydrophone that is sensitive to acoustic pressure signals while rejecting variations in other quantities such as temperature, static pressure, or platform vibrations. One way to overcome this problem is to design fiber-optic interferometric hydrophones in which both legs of the interferometer are active and respond to pressure with strains of opposite sign. This talk will demonstrate the application of this “push-pull” design philosophy to bidirectional and omnidirectional hydrophones by describing several hydrophones that were developed at the Naval Postgraduate School. One bidirectional hydrophone measures the fluid-induced motion of a neutrally buoyant seismic sensor. The omnidirectional hydrophones create a push-pull strain using a flexural disk or a flextensional method. The dual-plate, four-coil, flexural disk hydrophone detects sound by measuring the surface strain on the two circular end caps of an air-backed cylinder. The use of two disks doubles the sensitivity to pressure while canceling any acceleration induced response. The flextensional hydrophone measures the difference between the strains in the equatorial and meridional circumferences induced when an oblate spheroidal shell is subject to a change in pressure. [Work supported by the Naval Sea Systems Command.]