This book constitutes the thoroughly refereed conference proceedings of the 12th International Conference on Cognitive Radio Oriented Wireless Networks, CROWNCOM 2017, held in Lisbon, Portugal, in September 2017. The 28 revised full papers presented were carefully reviewed and selected from numerous submissions and cover the evolution of cognitive radio technology pertaining to 5G networks. The papers are clustered to topics on spectrum management; network management; trials, test beds, and tools; PHY and sensing; spectrum management.