Introduction to the special issue on the 2011 Joint IEEE International Frequency Control Symposium and European Frequency and Time Forum

We are pleased to introduce this special issue of the IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control commemorating the 2011 joint meeting of the IEEE International Frequency Control Symposium and the European Frequency and Time Forum. This conference, held in San Francisco, California, was the fifth in a series of successful joint meetings bringing together the world´s experts in all domains of time and frequency. In 2011, the joint conference consisted of a set of 12 tutorials held on the first day and 3 parallel tracks held over the next 4 days. It also included a plenary session, a poster session, a student paper competition, a panel session, and a technical exhibition. There were approximately 500 attendees, who saw more than 280 presentations across the following 6 topical areas: 1) Materials and Resonators; 2) Oscillators, Synthesizers, and Noise; 3) Microwave Frequency Standards; 4) Sensors and Transducers; 5) Timekeeping and Time and Frequency Transfer; and 6) Optical Frequency Standards. All of these topics are represented in this special issue by 8 invited and 17 contributed papers.The 8 invited and 17 contributed papers in this special issue focus on the following topical areas covered at the 2011 Joint IEEE International Frequency Control Symposium and European Frequency and Time Forum, held in San Francisco, California: 1) Materials and Resonators; 2) Oscillators, Synthesizers, and Noise; 3) Microwave Frequency Standards; 4) Sensors and Transducers; 5) Timekeeping and Time and Frequency Transfer; and 6) Optical Frequency Standards.