Cognitive Radio Sensor Network is a recently emerging paradigm that aims to utilize the unique features provided by the Cognitive Radio concept to incorporate additional capabilities in existing Wireless Sensor Networks. Wireless sensor networks operate in licensed bands. Due to tremendous growth in other band technologies, namely Bluetooth, , , and so on, wireless sensor networks need additional capabilities to combat the interference caused by them. Usage of opportunistic spectrum access capability offered by Cognitive Radio technology can be the optimal approach to address this issue. However, adoption of cognitive radio concepts in wireless sensor networks can impose added challenges and requirements. In this chapter, a comprehensive survey oF challenges, requirements, and applications of cognitive radio sensor networks is presented. Further, the node level and network level modifications made in the architecture of wireless sensor networks is also detailed in order to provide understanding of spectrum management and power optimization in cognitive radio sensor networks.