The increasing need for functional flexibility (the number of wireless standards is large and expected to grow) and the exploding cost of system-on-chip design will make implementation of wireless standards on reconfigurable radios the only viable option in the future. Software Defined Radios (SDRs) will offer higher flexibility at lower cost. Moreover, they are key enablers in the realization of cognitive radios, which will enable more efficient use of network and spectral resources. Green SDRs will be essential, to save on crucial and scarce resources: energy and spectrum. 'Green Software Defined Radios' gives insight in the trends asking for green SDRs.