In this chapter, a number of different spectrum trading models based on economic theory are presented. In the first model, dynamic competitive spectrum sharing is modeled as a Cournot competition, which is formulated as static and dynamic non-cooperative games. From this competition, given the pricing function adopted by the primary user, the optimal amount of spectrum for secondary users needs to be determined so that the utility of each of the secondary users is maximized. In the second model, competitive spectrum pricing among primary users (or service providers) is modeled as a Bertrand competition where multiple primary service providers sell the available spectrum opportunities to a secondary service provider. The third model is a cooperative pricing model for which spectrum pricing can be obtained as the solution of an optimization model solved by a central controller. Another model is the market-equilibrium pricing model in which there is neither competition nor cooperation among primary service providers. A comparison between market-equilibrium, competitive, and cooperative spectrum pricing is presented. The characteristics of these pricing schemes are qualitatively and quantitatively compared. Also, competitive spectrum pricing in the Bertrand model is formulated as a repeated game to investigate the long-term behavior of the primary service providers. In this case, if a punishment mechanism is used and the primary service providers properly weigh their profits in the future, a collusion can be maintained to achieve the highest profit for all primary service providers. To this end, a hierarchical framework for spectrum trading in IEEE 802.22 WRANs is presented. This framework consists of a double auction model, a non-cooperative game model, and an evolutionary game model.