Phased arrays have been traditionally used in military applications for several decades. Recent growth in civilian radar-based sensors and communication systems has drawn increasing interest in utilizing phased array technology for commercial applications. Despite the broad range of potential phased array applications, phased array technology has not been widely deployed in the commercial arena. The high cost and complexity of phased arrays is the primary impediment to their deployment in any large-scale commercial application. In order to deploy phased arrays in a wide range of applications, ongoing efforts are underway to develop new architectures that allow complexity of phased array to be reduced. In this book, conventional designs of phased arrays are reviewed and various new approaches are presented to realize phased arrays with reduced complexity.