This Course on Metrology and Fundamental Constants was held in Varenna in July 2006 and was organised by the Italian Physical Society, the Istituto Nazionale di Ricerca Metrologica of Italy (INRIM), and the Bureau International des Poids et Mesures. Co-incidentally 2006 marks the first year of the existence of INRIM, the new Metrological Institution of Italy, resulting from the merging of the Istituto di Metrologia “Gustavo Colonnetti” (IMGC) and the Istituto Elettrotecnico Nazionale “Galileo Ferraris” (IEN).

Besides this particular event, the School in Varenna, as well as the Summer School on Metrology organized by the BIPM in Paris, is justified by three facts, the need to provide, from time to time, a co-ordinated set of lectures which present the relevant progress in Metrology, the increasing intertwining between Fundamental Physics and the practice of Metrological Measurements, and, third, the flurry of new and unexpected discoveries in this field, with a correlated series of Nobel Prizes bestowed to individuals working in Fundamental Constants research and novel experimental methods.

This is the fourth of the Enrico Fermi Schools on Metrology and Fundamental Constants organized by the Italian Physical Society. The first was held in 1976, the second and the third respectively in 1989 and 2000, all of which were supported by the direct presence of BIPM via the Director pro tempore and the strong presence of the National Metrological Laboratories. This presence was felt in two ways, first by sending many of their experts as lecturers and, secondly, by supporting the attendance of a large number of their researchers at the School.

One of the most fascinating and exciting characteristics of metrology is its intimate relationship between fundamental physics and the leading edge of technology which is needed to perform advanced and challenging experiments and measurements, as well as the determination of the values and interrelations between the Fundamental Constants.

In some cases, such as the caesium fountains clocks or the optical frequency standards, the definition of the value of a quantity is, in the laboratory, in the region of 10⁻¹⁶ and experiments are under way to reach 10⁻¹⁸.

Many of these results and the avenues leading to further advances were discussed during the School, along a major step in metrology, expected in the near future, which could change the “old” definition of the kilogram, still based on a mechanical artefact, toward a new definition resting on a fixed value of a fundamental constant. The current possibilities include a fixed value of the Planck Constants or the Avogadro Number. Several National Metrological Institutes (NMIs) and other organizations are collaborating, worldwide, in the International Avogadro Consortium, and a number of NMIs are involved in the so-called “Watt balance” in the mechanical watt ( measurement of a force and of a speed ) is directly compared with the electrical watt in the same device (measured via Josephson and von Klitzing effects) and which would led to a measurement of the Planck Constant.

The success of this fourth Course was made possible by the close co-operation and the dedication of many Institutions and individuals.

The Directors wish to thank the Italian Physical Society and the INRIM for having provided the financial support for the organization of the School and for the attendance of several student. Of the some seventy or so students attending the School, two thirds were supported by their parent Institution, and the others directly by the School.

The Directors also wish to express their warm thanks to all the lecturers and seminar speakers who offered their expertise to the students, not only during the scheduled lectures, but also by being available for discussions and seminars; their enthusiasm and competence were crucial elements for ths success of the school and were duly appreciated by the students.

A particular debt of gratitude must be expressed to Maria Luisa Rastello who acted as Scientific Secretary of the School, mainly in the three-year period needed to prepare and to organize the school. During the same period the Directors met on a number of times to optimise the program and to identify the Speakers to be invited.

Finally the extremely valuable help and the friendly co-operation of Mrs. Barbara Alzani and Carmen Vasini acting on behalf of SIF must be acknowledged.

The Directors hope that the friendship created, as well as the information shared, will be valuable elements in building the students' future careers. For many metrologists, attendance at a the Varenna school is a seminal point in their training and development. The Directors look forward to seeing many of the 2006 students appear in the future as leaders and specialists in their fields. If the school has played even a small part in this, we shall have achieved our aim.

T. Hänsch, S. Leschiutta and A. J. Wallard