Cognitive radio and networks is the key to futuristic reconfigurable communication and networking. Apart from efficient use of the spectrum, they can facilitate the integration of different wireless systems and their appropriate usage based on the communication environment and application requirements. The Cognitive Radio Network (CRN) formed out of cognitive radios extends the radio link-level features to network layer functions and above. Some of the primary tasks of CRN (as pointed by Haykin) include: to perceive the radio environment by empowering each user’s receiver to sense the environment on a continuous-time basis; to learn from the environment and adapt the performance of each transceiver to statistical variations in the incoming RF stimuli; to facilitate communication between multiple users through cooperation in a self-organized manner; to control the communication processes among competing users through the proper allocation of available resources; to create the experience of intentions and self-awareness. These tasks open up many technical challenges encompassing devices, protocols and applications.