Cognitive radio has emerged as a promising technology for maximizing the utilization of the limited radio bandwidth while accommodating the increasing amount of services and applications in the wireless networks. This book presents a unified view of cognitive radio technology (both theory and practice). It includes a set of research and survey articles from world-class researchers featuring the recent advances in theory and applications of cognitive radio technology for the next generation (e.g., fourth generation) wireless communication networks. The contributed articles cover both the theoretical concepts (e.g., information-theoretic analysis) and system-level implementation issues. Therefore, the book provides a unified view on the state-of-the-art of cognitive radio technology and the rich set of references in each of the articles will be invaluable to researchers.