This book provides a broad introduction to Cognitive radio, which attempts to mimic human cognition and reasoning applied to software defined radio and reconfigurable radio over wireless networks. It provides readers with significant technical and practical insights into different aspects of Cognitive radio, starting from a basic background, the principle behind the technology, the inter-related technologies and application to cellular and vehicular networks, the technical challenges, implementation and future trends. The discussion balances theoretical concepts and practical implementation. Wherever feasible, the different concepts explained are linked to application of the corresponding scheme in a particular wireless standard.