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 the underlying continuous-time system is usually forgotten once the samples are tak­ en. The alternative point of view, adopted in this book, is to formulate the analy­ sis in such a way that the user is constantly reminded of the presence of the under­ lying continuous-time signals. We thus give emphasis to two aspects of sampled-data analysis: Firstly, we formulate the various algorithms so that the appropriate contin­ uous-time case is approached as the sampling rate increases. Secondly we place emphasis on the continuous-time output response rath­ er than simply focusing on the sampled response.