Aperiodic'94 took place in Les Diablerets (Switzerland) from 18 to 22 September 1994. Close to 150 participants from all over the world made the trip to this alpine resort dominated by a glacier. Thanks to the generosity of many scientific organizations in Switzerland, the University of Lausanne, the International Union of Crystallography and the Soros Foundation, it was possible to invite many scientists and young scientists from countries with hard currency problems. No less than 60 participants could be invited or partially supported.

Aperiodic '94 continued the tradition inaugurated by the former series of International Conferences on Modulated Structures, Polytypes and Quasicrystals (MOSPOQ) which were held in Marseille (1984), Wroclav (1986), Varanasi (1988) and Balatonszéplak (1991). The conference was organised in close collaboration with the IUCr Commission on Aperiodic Crystals. Following its terms of reference, the Commission is responsible for the organization of future meetings on a triennial basis in alternation with the International Conference on Quasicrystals and is intended to promote the development of common methods and nomenclature for the crystallographic investigation of aperiodic crystals including modulated structures, polytypes, incommensurate misfit or composite crystals and quasicrystals. It is also the aim of the series of conferences to promote scientific interchange among groups working in various fields of aperiodic materials and to emphasise the multidisciplinary aspects of aperiodicity.

The meeting in Les Diablerets indeed covered the broad spectrum of aperiodicity. The field of quasicrystal structures was addressed by many speakers. In particular Christian Janot (Grenoble) and Walter Steurer (Zürich) presented respectively the fields of icosahedral and decagonal phases. Ken Kelton (St Louis) underlined the importance of titanium based quasicrystals. We all enjoyed the presentation of Jean-Marie Dubois (Nancy) who explained to the audience the specific physical properties of quasi crystals and some potential applications. Kenji Hiraga (Sendai) presented recent studies on decagonal quasi crystals and crystalline phases by high-resolution electron microscopy.

The field of incommensurate structures was also very well represented. Volker Heine (Cambridge, UK) presented some convincing models for the origin of incommensurate structures in silicate minerals and plagioclase feldspars. Krzysztof Parlinski (Krakov) described very interesting computer simulations of phase transition mechanisms involving commensurate and incommensurate phases. Structural models for the incommensurate bismuth high Tc superconductors were presented by Mike Walker (Toronto). Valérie Bussien Gaillard (Lausanne) showed the interesting case of an incommensurate organic compound which dramatically revealed the limits of the concepts presently accepted in the field of incommensurate modulated structure analysis. The state of the art in optical studies in incommensurate crystals was presented by Jesus Etxebarria (Bilbao). Orest Vlokh (Lviv) described further the optical properties of crystals with incommensurate structures. The field of incommensurate intergrowth compounds and composite crystal structures was presented by Sander Van Smaalen (Groningen) and Akiji Yamamoto (Tsukuba). They revealed how the concept of superspace group can be applied to describe these types of material. Dhananjai Pandey (Varanasi), Alain Baronnet (Marseille) and Juliana Grell (Berlin) presented the current state of research in the field of polytypes, polytypism and OD layer structures. Jean-Michel Kiat (Saclay) presented a survey of the intricate field of premartensitic anomalies in diffraction-diffusion experiments.

The conference also gave mathematicians the opportunity to present future trends in non periodic structure research. Ludwig Danzer (Dortmund) presented some new directions in aperiodic tilings including a very interesting three dimensional prototile that can fill space without any translation. Peter Kramer (Tübingen) introduced the audience to non-commutative crystallography with potential applications in quasi periodic tilings. The participants had the opportunity to glimpse at future trends through the visions of Alan Mackay (London) who presented some new ideas in 'non-conformist crystallography'. Another approach was presented by Aloysio Janner (Nijmegen) and Ravil Galiulin (Moscow) who revealed some interesting aspects of non-Euclidean symmetry which can be discovered in crystal structures.

Many more interesting oral and poster presentations were given during the conference. Two poster sessions, each lasting for two days, were organised. The posters were well attended even in the evening after dinner. Thanks to the excellent work of the local committee and the well-functioning equipment of the congress hall, the conference went smoothly from the beginning to the end. Each participant could have access to Internet with the help of more than ten terminals, workstations, PCs and Macintoshs.

The social program included an evening concert with alpenhorn and piano. The participants were able to enjoy this unexpected ensemble in a typical alpine surrounding. A visit to the wonderful Giannada museum in Martigny gave some insight into the famous roman city which is still under excavation. In the evening dinner, participants had the opportunity to taste the "raclette", a typical local speciality based on mountain cheese.

This conference was probably the first of its kind to take full advantage of the services offered by Internet. All the abstracts were available on a WWW server often the same day after reception. The program committee and the organizers could quickly exchange their information without delay. Most participants took advantage of these services e.g. by contacting other participants or the organizers prior to the meeting. The complete information on the conference including this report is available at URL http://www.unige.ch/crystal/aperiodic/mtg-ch94-index.html. The proceedings of the meeting will be published at the beginning of next year by World Scientific in Singapore: Aperiodic'94, edited by G. Chapuis and W. Paciorek (World Scientific, Singapore, 1995) ISBN 981-02-2080-4.

Gervais Chapuis