The interactions of acoustic waves and thermoviscous fluids in closed cavities lead to some important physical phenomena such as, linear and nonlinear standing waves, and acoustic streaming which are very important in a wide range of engineering applications. This book focuses on the detailed investigations of the standing wave dynamics in resonant cavities. As a part of the book, novel numerical and experimental techniques are presented to analyze different phenomena caused by acoustic- fluid interactions. Using these techniques, the behavior of pressure, acoustic and streaming velocity fields inside resonators are investigated. Furthermore, the novel ideas of valveless standing wave pump and micropump are discussed and their performance are analyzed numerically and experimentally.