The objective of this paper is to show that time-reversal invariance can be exploited in acoustics to accurately control wave propagation through complex media and create a variety of useful instruments. To illustrate the robustness of time reversal mirrors, several experiments conducted in multiply scattering media, in waveguides and in reverberant cavities are presented. They show that, contrary to long-held beliefs, multi pathing and multiple scattering enhances resolution in time reversal focusing, by making the effective size of the time reversal mirror much larger than its physical size. Applications of time-reversal mirrors in pulse echo detection and particularly in nondestructive testing will be discussed. ©2001 American Institute of Physics.