The unparalleled evolution of wireless communications is reflected in the tremendous investments on research and development, targeted at the continuous introduction of innovations that could serve the information society. This has led to the coexistence and complementary exploitation of versatile, legacy and also emerging Radio Access Technologies (RATs), such as: wireless wide area networks (such as 2G/2.5G/3G/3G+ mobile communications, the IEEE 802.16 suite and WiMAX), broadcasting technologies, wireless short range networks (such as WLANs/WPANs and wireless sensor networks). Moreover, the wireless world is currently migrating towards the B3G (Beyond the 3rd Generation) era. In the B3G era, network operators (NOs) will have to address increased complexity due to the heterogeneity of the network and terminal infrastructure, the ever-increasing user requirements, the co-existence and need for complementary exploitation of various RATs. A NO should rely on different RATs for raising the customer satisfaction, and achieving the required Quality of Service (QoS) levels, cost-effectively.

An option for handling complexity is to enhance B3G infrastructures with "cognitive networking" capabilities. A cognitive wireless networks should be capable of dynamically selecting its behaviour (configuration), through management functionality that takes into account the context of operation, goals and policies, profiles (of applications, users, terminals and network elements), and past experience and knowledge (acquired through machine learning techniques).

In response to the above, it becomes of primary importance to define, develop and validate management functionality that will lead us to the era of cognitive B3G wireless networks and systems. Therefore, this special issue welcomes contributions presenting advances in research areas, such as:

• Management functionality for cognitive wireless wide area networks
• Management functionality for cognition in short range networks
• Context acquisition, sensing, reasoning
• Policy based management of heterogeneous B3G wireless infrastructures.
• Autonomic (self-*) functionalities for cognitive elements, terminals, networks
• Collaborative spectrum and power management, negotiation strategies
• Pilot channels, standardisation and regulation aspects for cognitive infrastructures
• Algorithms for cognitive wireless networks and systems
• Proof of concept and validation