Cognitive Radio (CR) enables dynamic spectrum access to utilize licensed spectrum when it is idle. CR technology is applied to wireless ad hoc and sensor networks, to form Cognitive Radio Ad Hoc Networks (CRAHNs) and Cognitive Radio Sensor Networks (CRSNs), respectively. Clustering is an efficient topology management technique to regulate communication and allocate spectrum resources by CR capabilities of nodes in CRAHNs and CRSNs. In this paper, we thoroughly investigate benefits and

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... ities of clustering such as topology, spectrum and energy management in these networks. We also overview motivations for and challenges of clustering in CRAHNs and CRSNs. Existing clustering schemes are reviewed and compared. We conclude by revealing key considerations and possible solutions for spectrum-aware clustering in multi-channel CRAHNs and CRSNs. Index Terms-spectrum-awareness, clustering, multi-channel, cognitive radio, ad hoc networks, sensor networks. M. Ozger is with Next-generation and Wireless Communications Laboratory (NWCL),