Time reversal (TR) is a signal processing technique that can be used to focus high amplitude sound or vibration at a desired location. TR focusing can be done with sources placed far from the desired focal location and the technique excels in complex environments. The impulse response between each source and the desired focal location must be obtained prior to the focusing and the environment must remain relatively unchanged for successful focusing. Multiple scattering or reverberation of waves off of many reflecting surfaces in the environment can actually be used advantageously by exploiting those reflections as additional image sources. This talk will provide an introduction to TR and then focus on the use of TR to provide high amplitude focusing of sound and vibration. Applications of high amplitude TR include lithotripsy of kidney stones, histotripsy of lesions, and locating cracks and defects in structures such as in human teeth, spent nuclear fuel storage casks, airplane wings, and automotive bearing caps. Recently, high amplitude TR of airborne sound has been studied in a reverberation chamber to generate a focused difference frequency and to study the nonlinear acoustics of the peak sound levels of 200 dB that have been attained.