It is our great pleasure and singular honor to introduce this Special Section of the IET Journal on Radar, Sonar & Navigation, dedicated to the Fifth International Waveform Diversity and Design Conference (WDD) that was held in Niagara Falls Canada from 3??10 August 2010. WDD is an international conference devoted to bringing together researchers and technologists from diverse backgrounds and specialties to facilitate the exchange of ideas, research, and technologies for dynamically adapting waveforms to their propagation environments. Specific objectives include developing analytical methodologies and new hardware technologies for system applications in sensors, communications, navigation, and countermeasures.