Recent technological advances in high-frequency (>10 kHz) sonar transducers, sonar transceivers, and sonar design have been accompanied by increased capabilities for observing ocean phenomena. These advances include the high range resolution and frequency-domain target classification capabilities associated with wideband acoustic echo sounders, the long-range high-resolution synoptic imaging capabilities associated with multibeam echo sounders and synthetic aperture sonar, and an increased focus on sensor calibration for all systems. High-frequency sonars are increasingly being used to quantify ocean phenomena at scales ranging from sub-centimeter (e.g., individual gas bubbles) to 100s of km (e.g., internal waves) to several 10s of km (e.g., thermohaline staircases). In this talk, we highlight some of the ocean processes that we have been investigating using high-frequency sonar systems, typically involving the transport of hydrocarbons, heat, energy, and fresh water into and through the ocean, and some of the (many) acoustic challenges that must be overcome to continue to increase the value of these observations.