The papers in this volume aim to represent the most up-to-date research contributions on the observations, theoretical interpretations, and empirical and physical models of variations observed in solar and stellar irradiances, as well as on Sun-climate connections. Both theoretical studies and irradiance observations show that the energy output of the Sun and solar-type stars varies, changing on time scales related to the short-term surface manifestations of solar/stellar magnetic activity as well as long-term modulations driven by processes in the interiors of the stars. Papers presented in this book point out that at the Earth these variations influence the terrestrial climate, radiative environment and upper atmospheric chemistry.

These Proceedings result from the papers and discussions of the U.S.-Japan Seminar "Recent Advances in the Understanding of Solar Flares" held in Tokyo October 5-8, 1982. The meeting was sponsored jointly by the Japan Society for the Promotion of Science and the u.S. National Science Foundation. The principal aim of the meeting was to obtain the most up-to-date physical picture of solar flares by bringing together results from the recent observations by the Solar Maximum Mission (SMM) and HINOTORI satellites, together with other satellite data and ground-based data at both optical and radio wavelengths. These data cover the recent maximum of the solar activity cycle. The SMM and HINOTORI introduced a new dimension in flare observations by carrying out the first hard X-ray imaging observations, and the organizers especially felt that an intense discussion of the significance of these results in the context of flare theories would be important. Starting with an introductory presentation of the characteristics of the instruments on board the satellites, the sessions of the first day and the beginning of the second dealt mainly with energy transport in flares and with .the formation process of the hot plasma which is .

The IAU Colloquium No. 143 "The Sun as a Variable Star: Solar and Stellar Irradiance Variations" was held on June 20 - 25, 1993 at the Clarion Harvest House, Boulder, Colorado, USA. The main objective of this Colloquium was to review the most recent results on the observations, theoretical interpreta tions, and empirical and physical models of the variations observed in solar and stellar irradiances. A special emphasis of the Colloquium was to discuss the results gained on the climatic impact of solar irradiance variability. The study of changes in solar and stellar irradiances has been of high interest for a long time. Determining the absolute value of the luminosity of stars with different ages is a crucial question for the theory of stellar evolu tion and energy production of stellar interiors. Observations of the temporal changes of solar and stellar irradiances - in the entire spectral band and at different wavelengths - provide an additional tool for studying the physical processes below the photosphere and in the solar- stellar atmospheres. Since the Sun's radiative output is the main driver of the physical processes with in the Earth's atmosphere, the study of irradiance changes is an extremely important issue for climatic studies as well. Climatic models show that small, but persistent changes in solar irradiance may influence the Earth's climate.

These are the Proceedings of Colloquium No. 153 of the International Astro nomical Union, held at Makuhari near Tokyo on May 22 - 26, 1995, and hosted by the National Astronomical Observatory. This meeting was intended to be an interdisciplinary meeting between re searchers of solar and stellar activity, in order for them to exchange the newest information in each field. While each of these areas has seen remarkable advances in recent years, and while the researchers in each field have felt that information from the other's domain would be extremely useful in their own work, there have not been very many opportunities for intensive exchanges of information between these closely related fields. We therefore expected much from this meeting in pro viding stellar researchers with new results of research on the counterparts of their targets of research, spatially and temporarily resolved, as observed on the Sun. Likewise we hoped to provide solar researchers with new results on gigantic ver sions of their targets of research under the very different physical circumstances on other active stars. It was our greatest pleasure that we had wide attendance of experts and active researchers of both research fields from all over the world. This led to extremely interesting talks and very lively discussions, thereby stimulating the exchange of ideas across the fields.