In this introductory talk to time reversal I will discuss experiments conducted during the past ten years in the context of ultrasounds and underwater acoustics. I will present applications to imaging, detection and communications for which waves are propagating in inhomogeneous media. I will explain how randomness is naturally used to model these media and understand mathematically the refocusing and super-resolution effects observed in time reversal experiments. Movies on time reversal can be seen on my web page, as well as an article in pdf by Mathias Fink in Scientific American (November 1999).