Undoubtably one of the key factors influencing recent technology has been the advent of high speed computational tools. Virtually every advanced engi­ neering system we come in contact with these days depends upon some form of sampling and digital signal processing. Well known examples are digital tele­ phone systems, digital recording of audio signals and computer control. These developments have been matched by the appearance of a plethora of books which explain a variety of analysis, synthesis and design tools applica­ ble to sampled-data systems. The reader might therefore wonder what is distinc­ tive about the current book. Our observation of the existing literature is that