The reforms in spectrum management aim toward more efficient, flexible, and shared use of spectrum, while fostering innovation and competition in mobile communications. The goal is to have affordable wireless broadband and make Internet access a human right. To achieve this goal, the regulators need to identify, evaluate, and decide between the different spectrum access models. This article presents a taxonomy of the models, which is based on priorities between the different users of spectrum. For example, the low priority systems may be allowed to use the spectrum only if the high priority systems are not occupying the frequency. The hierarchy of the systems can be implemented using different technologies such as centralized databases or distributed sensing devices. The taxonomy clarifies the regulatory alternatives and emphasizes the differences in ownership and usage rights. The new models can be incorporated in the auction design in order to estimate their value to the companies, and this reflects the recent trend of supporting spectrum management with market-based methods.