We argue for a policy-based approach to increase spectrum availability. We have designed a language to capture rules and regulations for opportunistic spectrum use. A Policy Reasoner that reasons about these spectrumsharing policies can be used with cognitive radios to guarantee policy-specified behaviors. We demonstrate the reasoner on various policies, including those established for the dedicated spectrum from the Commisssion for Communication Regulations that has been acquired for DySPAN 2007. We show the effects of enforcing these policies and how a radio adapts to the conditions of dynamically changing environments. We will link our reasoner to a live sensor from Rockwell Collins that measures the state of the spectrum at the conference site and delivers input data for the reasoner. We will also illustrate the ease of changing policies and uploading new policies.