This book is intended as an introduction to array signal process­ ing, where the principal objectives are to make use of the available multiple sensor information in an efficient manner to detect and possi­ bly estimate the signals and their parameters present in the scene. The advantages of using an array in place of a single receiver have extended its applicability into many fields including radar, sonar, com­ munications, astronomy, seismology and ultrasonics. The primary emphasis here is to focus on the detection problem and the estimation problem from a signal processing viewpoint. Most of the contents are derived from readily available sources in the literature, although a cer­ tain amount of original material has been included. This book can be used both as a graduate textbook and as a reference book for engineers and researchers. The material presented here can be readily understood by readers having a back­ ground in basic probability theory and stochastic processes. A prelim­ inary course in detection and estimation theory, though not essential, may make the reading easy. In fact this book can be used in a one semester course following probability theory and stochastic processes.