The radio spectrum is the fundamental resource upon which all radiocommunication services depend. It is utilised for a vast array of different services over land, sea, air and space, and brings an enormous benefit to society. However, it also brings stringent demands for its management, at both national and international levels, in order to ensure that the services that have been allocated bands are not subjected to interference. Current methods of radio spectrum management are based around rigid, fixed allocations of bands for use by particular services. The demand for the spectrum is increasing, but the levels of spectrum available are not matching the demand. This is compounded by the convergence of radio systems, which makes the allocation of bands for precisely defined categories of service appear less relevant. Therefore, current radio spectrum management is faced with a need to improve the efficiency of spectrum use, and adapt to the challenges imposed by convergence. This thesis presents and investigates a new method for utilising spectrum that is cooperatively shared between two radio systems. Most radio systems are subject to inherent time-varying demands for their spectral resources, and it is proposed that these variations can be exploited, together with the coordination enabled through a converged multi-radio system, to improve the efficiency of spectrum usage. This is studied on several levels. A theoretical model for the potential spectrum efficiency gains achievable from the time-varying demands on the networks is derived. An algorithm is developed to reallocate the spectrum dynamically to the networks, and different aspects of this algorithm are investigated by simulation to analyse its performance. Furthermore, the impact of external factors, outside of the algorithm’s control, is studied, to observe the effect on the performance. Finally, the results of the simulated investigations are brought together, and compared to the theoretical model.