Modern Applications of Acoustics is a series,that will, in the hopes of the editors, present the most exciting developments in the applications of acoustics that have emerged in the past few decades. This first seven-author volume, which was already nearing publication when the series was conceived, is an auspicious beginning. It can be argued that all living entities have their own built-in biological acoustic sensors, be they aural or tactile, whose sensitivity, in some instances, is at the optimum signal-to-noise level. For instance, it is known that if the human ear were any more sensitive, Brownian noise would mask the intelligibility of perceived sound. It is possible that the sound emitted by crackling dry leaves and twigs may be the first artificial sensors devised by humans for detecting game or intruders. The sensors described in this volume avail themselves of the most modern microphotolithographic techniques, and use sophisticated signal processing techniques that could not be achieved without the use of the formidable power of modern computers. But, the germinal ideas are the product of human ingenuity.