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The NATO Advanced Study Institute on Physios of St~ong Fields was held at Maratea/Italy from 1-14 June, 1986. The school was devoted to the advances, theoretical and experimental, in physics of strong fields made during the past five years. The topic of the first week was almost exclusively quantum electrodynamics, with dis­ cussions of symmetry breaking in the ground state, of the physics of strong fields in heavy ion collisions and of precision tests of perturba­ tive quantum electrodynamics. The famous positron lines found at GSI (Darmstadt) and the related question'new particle versus vacuum decay'- (yes or no or both) - constituted the center of experimental advances. This was followed in the second week by the presentation of a broad range of other areas where strong fields occur, reaching from nuclear physics over quantum chromodynamics to gravitation theory and astrophysics. We were fortunate to be able to calIon a body of lecturers who not only made considerable personal contributions to this research but who are also noted for their lecturing skills. Their enthusiasm and dedication for their work was readily transmitted to the students resulting in a very suc­ cessful school.

Topological defects formed at symmetry-breaking phase transitions play an important role in many different fields of physics. They appear in many condensed-matter systems at low temperature; examples include vortices in superfluid helium-4, a rich variety of defects in helium-3, quantized mag­ netic flux tubes in type-II superconductors, and disclination lines and other defects in liquid crystals. In cosmology, unified gauge theories of particle interactions suggest a sequence of phase transitions in the very early uni­ verse some of which may lead to defect formation. In astrophysics, defects play an important role in the dynamics of neutron stars. In 1997 the European Science Foundation started the scientific network'Topological defects'headed by Tom Kibble. This network has provided us with a unique opportunity of establishing a collaboration between the representatives of these very different branches of modern physics. The NATO-ASI (Advanced Study Institute), held in Les Houches in February 1999 thanks to the support of the Scientific Division of NATO, the European Science Foundation and the CNRS, represents a key event of this ESF network. It brought together participants from widely different fields, with diverse expertise and vocabulary, fostering the exchange of ideas. The lectures given by particle physicists, cosmologists and condensed matter physicists are the result of the fruitful collaborations established since 1997 between groups in several European countries and in the U.S.A.

This meeting discussed the experimental results and theoretical aspects in the field of high energy physics, with special reference to the top quark observation, heavy flavor physics and symmetry-breaking mechanisms. The major topics are developed in a series of course lectures.

This volume contains the talks given at the above workshop which was devoted to discussing the newest developments in various models of electroweak symmetry breaking forming the basis of modern particle physics. It includes various aspects of Higgs physics and condensate models embodying dynamical symmetry breaking.

This is the first systematic volume which presents a detailed introduction to every facet of the modern version of Dynamical Symmetry Breaking which has been rapidly developed in recent years. Most of the lectures are given by pioneers in this new field and are geared mainly to the level of second year graduate students.

The papers presented here focus on new developments in both theoretical and phenomenological aspects of standard theory, with an emphasis on understanding of the mechanism of electroweak symmetry breaking. This workshop covers the formal aspects and the related new models of electroweak symmetry breaking and the present status of the Standard Model.