In this volume, which was originally published in 1996, isy information is studied in the context of computational complexity; in other words the text deals with the computational complexity of mathematical problems for which information is partial, isy and priced. The author develops a general theory of computational complexity of continuous problems with isy information and gives a number of applications; deterministic as well as stochastic ise is considered. He presents optimal algorithms, optimal information, and complexity bounds in different settings: worst case, average case, mixed worst-average and average-worst, and asymptotic. The book integrates the work of researchers in such areas as computational complexity, approximation theory and statistics, and includes many fresh results as well. About two hundred exercises are supplied with a view to increasing the reader's understanding of the subject. The text will be of interest to professional computer scientists, statisticians, applied mathematicians, engineers, control theorists, and ecomists.