Acoustic pressure measurements with hydrophones are critical to characterize safety and effectiveness of diagnostic and therapeutic medical ultrasound devices. This tutorial will cover (1) fundamental interactions between ultrasound and biologic tissues that determine thresholds for safety and effectiveness, (2) underlying physics of various hydrophone designs (e.g., membrane, needle, capsule, reflection-type fiber optic, Fabry-Perot interferometric fiber optic), (3) fundamental hydrophone specifications, such as sensitivity, directivity, and effective sensitive element size, all of which are frequency-dependent, (4) pros and cons of each hydrophone design for different applications, (5) how to characterize hydrophone measurement uncertainty, and (6) deconvolution methods to remove distortions in pressure measurements due to frequency-dependent sensitivity and spatial averaging artifacts.