Dynamic spectrum sharing technique ( #x201C;Cognitive Radio #x201D;) where secondary users opportunistically utilize temporarily or locally unused spectrum has emerged as a prime candidate technology to relieve the perceived spectrum shortage. Making a realistic assessment of the amount of spectrum available for secondary services is the objective of the EU FP7 QUASAR project. In the project it is found to be fundamentally difficult to reliably determine which part of the spectrum is available, which leads to large safety margins consequently to poor spectrum utilization. Further, the business success of future systems depends on the scalability of the secondary access techniques. Also, the vast majorities of spectrum opportunities are highly localized in time and spaces and strongly dependent on the intended use such that they defy common models for spectrum trading.