Solar and stellar photospheres constitute the layers most accessible to observations, forming the interface between the interior and the outside of the stars. The solar atmosphere is a rich physics laboratory, in which the whole spectrum of radiative, dynamical, and magnetic processes that tranfer energy into space can be observed. As the fundamental processes take place on very small spatial scales, we need high· resolution observations to explore them. On the other hand the small-scale processes act together to form global properties of the sun, which have their origins in the solar interior. The rapid advances in observational techniques and theoreticallllodelling over the past decade made it very timely to bring together scientists from east and west to the first lAU Symposium on this topic. The physics of the photosphere involves complicated interactions between magnetic fields, convection, waves, and radiation. During the past decade our understanding of these gener ally small-scale structures and processes has been dramatically advanced. New instrumen tations, on ground and in space, have given us new means to study the granular convection. Diagnostic methods in Stokes polarimetry have allowed us to go beyond the limitations of spatial resolution to explore the structure and dynamics of the subarcsec magnetic struc tures. Extensive numerical simulations of the interaction between convection and magnetic fields using powerful supercomputers are providing deepened physical insight. Granulation, magnetic fields, and dynamo processes are being explored in the photospheres of other stars, guided by our improved understanding of the solar photosphere.

Leading experts present the current state of knowledge of the subject of magnetoconvection from the viewpoint of applied mathematics.

The widespread tendency in solar physics to divide the solar atmosphere into separate layers and to distinguish phenomena of solar activity from phenomena of the quiet Sun emphasizes the wide ranging diversity of physical conditions and events occurring in the solar atmosphere. This diversity spans the range from a neutral, essentially quiescent atmosphere to a highly ionized, violently convective atmosphere; from a domain in which magnetic field effects are unimportant to a domain in which the magnetic pressure exceeds the gas pressure, and from a domain in which the particle motions are Maxwellian to a domain in which an appreciable fraction of the particles is accelerated to relativistic energies. It is now widely recognized that the chromosphere and corona have a common origin in the mechanical energy flux generated in the hydrogen convection zone lying beneath the photosphere. Furthermore, magnetic field phenomena appear to be as vital to the structure of th~ quiet Sun as to the active Sun. For these reasons it appears desirable to present a unified treatment of the entire solar atmosphere, both active and quiet, in a single volume. On the other hand, such a treatise must be very long if it is to avoid being superficial, and it is very difficult for a single author to write authoritatively on such a wide range of topics.

How are large-scale magnetic fields generated in the Sun in self-excited dynamo processes? And how are magnetic structures spontaneously formed in the Sun and how do they interact with the convective flows, storage and release of magnetic energy? These are just several of the fundamental questions answered in this timely review of our understanding of solar magnetic fields. This volume collects together review articles and research papers from an international conference, held in Freiburg, Germany, dedicated to the study of magnetic fields in the Sun. From large-scale patterns and global dynamo action to tiny flux tubes, from the overshoot layer below the convection zone up to the corona, and from instrumental problems and theoretical methods to the latest ground-based and satellite observations, this volume provides an essential review of our knowledge to date for graduate students and researchers.