This SpringerBrief focuses on spectrum trading designs in multi-hop cognitive radio networks. It starts with the motivation for spectrum trading and the review of existing spectrum trading designs. Then, it presents a novel CRN architecture for spectrum trading considering spectrum trading's economic features and wireless nature. Under this network architecture, it extends current single-hop per-user based spectrum trading design into a multi-hop transmission opportunity based one, and further into a session based one, while having economic properties guaranteed. This SpringerBrief not only provides a good review of current spectrum trading designs, it also touches on the cutting-edge interdisciplinary spectrum trading research on disparate fields of modeling, network architecture design, optimization theories, statistics, and economic theories. Advanced-level students studying computer science, electrical and computer engineering and economics, wireless network planners, and wireless spectrum engineers will find this book a useful tool.