This NATO Advanced Study Institute, held in Geilo between March 29th and April 9th 1981, was the sixth in a series devoted to the subject of phase transitions and instabilities. The present institute was intended to provide a forum for discussion of the importance of nonlinear phenomena associated with instabilities in systems as seemingly disparate as ferroelectrics and rotating buckets of oil. Ten years ago, at the first Geilo school, the report of a central peak in the fluctuation spectrum of SrTi0 close to its 3 106 K structural phase transition demonstrated that the simple soft-mode theory of such transitions was incomplete. The missing ingredient was the essential nonlinearity of the system. Parti cipants at this year's Geilo school heard assessments of a decade of experimental and theoretical effort which has been expended to elucidate the nature of this nonlinearity. The importance of order ed clusters and the walls which bound them was stressed in this con text. A specific type of wall, the soliton, was discussed by a number of speakers. New experimental results which purport to demonstrate the existence of solitons in a one-dimensional ferromagnet were presented. A detailed discussion was given of the role of solitons in transport phenomena in driven multistable systems, typified by a sine-Gordon chain."

This NATO Advanced Study Institute held at Gei10, Norway, April 16th-27th 1979, was the fifth in a series devoted to the subject of phase transitions and instabilities. The application to NATO for the funding of this ASI contained the following para graphs: "Traditionally one has made a clear distinction between solids and liquids in terms of positional order, one being long-ranged and the other at most short-ranged. In recent years experiments have revealed a much more faceted picture and a less sharp distinction between solids and liquids. As an example one now has 3-dimensiona1 (3-D) liquids with 1-D density waves and 3-D solids with 1-D-1iquid molecular chains. The subsystems have the common feature of 10w dimensional systems: a strong tendency for fluctuations to appear. Although the connection between fluctuations and dimensionality, and the suppression of long-range order by fluctuations, was pointed out as early as 1935 by Peier1s and by Landau, it is in the last five years or so that theoretical work has gained momentum. This development of understanding started ten years ago, however, much inspired by the experimental work on 2-D spin systems."

This volume comprises the proceedings of a NATO Advanced Study Institute held in Geilo, Norway, between 4 - 14 April 1989. This Institute was the tenth in a series held at Geilo on the subject of phase transitions. It was the first to be concerned with the growing area of soft condensed matter, which is neither ordinary solids nor ordinary liquids, but somewhere in between. The Institute brought together many lecturers, students and active researchers in the field from a wide range of NATO and some non-NATO countries, with financial support principally from the NATO Scientific Affairs Division but also from Institutt for energiteknikk, the Nor wegian Research Council for Science and the Humanities (NAVF), The Nordic Institute for Theoretical Atomic Physics (NORDITA), the Norwegian Physical Society and VISTA, a reserach cooperation between the Norwegian Academy of Science and Letters and Den norske stats oljeselskap a.s (STATOIL). The organizing committee would like to thank all these contributors for their help in promoting an exciting and rewarding meeting, and in doing so are confident that they echo the appreciation also of all the participants. 50ft condensed matter is characterized by weak interactions between polyatomic constituents, by important*thermal fluctuations effects, by mechanical softness and by a rich range of behaviours. The main emphasis at this Institute was on the fundamental collective physics, but prepar ation techniques and industrial applications were also considered.

Systems with competing energy scales are widespread and exhibit rich and subtle behaviour, although their systematic study is a relatively recent activity. This text presents lectures given at a NATO Advanced Study Institute reviewing the current knowledge and understanding of the subject, particularly with regard to phase transitions and dynamics, at an advanced tutorial level. Both general and specific aspects are considered, with competitions having several origins; differences in intrinsic interactions, interplay between intrinsic and extrinsic effects, such as geometry and disorder; irreversibility and non-equilibration. Among the specific physical application areas are supercooled liquids and glasses, high-temperature superconductors, flux or vortex pinning and motion, charge density waves, domain growth and coarsening, and electron solidification.