Network Coding (NC) is a technique used for effective and secure communication by improving the network capacity, throughput, efficiency, and robustness. In network coding, data packets are encoded by intermediate nodes and are then decoded at the destination nodes. Network coding has been successfully applied in a variety of networks including relay networks, peer-to-peer networks, wireless networks, cognitive radio networks, and wireless sensor networks. Cognitive radio network (CRN) is an emerging field which exploits the utilization of unused spectrum or white spaces, effectively and efficiently. In CRNs, network coding schemes are also applied to maximize the spectrum utilization, as well as to maintain the effective and secure transmission of data packets over the network. In this paper, we provide a comprehensive survey of network coding schemes in cognitive radio networks, highlighting the motivations for and the applications of network coding in CRNs. We provide typical case studies of network coding schemes in CRNs, as well as the taxonomy of network coding schemes in CRNs. Finally, we present open issues, challenges, and future research directions related with network coding in cognitive radio networks