Software Defined Radio (SDR) and Cognitive Radio (CR) could be in all radio transmitters sometime in the future. This thesis gives information about both SDR and CR and how we could use these technologies to utilize the scarce resources of frequencies. The use of CR in Dynamic Spectrum Access Networks could be a possible solution, and this thesis will try to give as much information as possible to this challenge. Information about Dynamic Spectrum Access and different challenges with this technology will be given. We will take a peek into research done in this field, and research in progress in this particular field.