S PECTRUM efficiency (SE) and energy efficiency (EE) are among the most important venues for technological advances in current and emerging wireless communication networks. The past decade has witnessed tremendous efforts and progress made by both the industry and academia for improving SE. We foresee that the emerging cognitive and self-organizing networks will further increase SE. In recent years, energy and power efficiencies of wireless networks have become more crucial because of the

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... ly rising energy cost and environmental concerns. While there has been a paradigm shift from improving SE to reducing energy consumption, a dilemma also arises as some EE criteria are in conflict with the SE objectives. Thus, there is an urgent need to address key challenges and state-of-the-art solutions for joint spectrum and energy efficient design (SEED) and optimization of wireless communication networks. With the above vision, a Call for Papers for a special issue in the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, was published in October 2011. The invited topics included system modeling, spectrum and energy efficient architectures and topologies for wireless networks, self-organization and self-optimization techniques for spectrum and energy efficient wireless networks, spectrum and energy efficient link adaptation and resource allocation, multiuser/single-user MIMO techniques for spectrum and energy efficiencies, and signal processing challenges for spectrum and energy efficient wireless networks. By the deadline in April 2012, we received 82 manuscripts, out of which 26 were accepted after a thorough and rigorous review process and 4 were suggested to accept if room. 1 Unfortunately, due to space constraints, several high-quality manuscripts could not be accommodated in this JSAC issue. Further, due to the page Y. Yang is with the