The aim of this Advanced Study Institute was to give an account on the most recent results obtained in solar research. Bucharest was chosen to host it, because the capital city of Romania was located right in the middle of the totality path of the last eclipse of the millennium, on 11th August 1999; furthermore the phenomenon was close to reach there its longest duration: 2m 23s. Such a total eclipse is not only a very spectacular event which draws the crowds: to astronomers, solar eclipses still offer the best conditions for observing the lower part of the corona. The Sun plays a crucial role in our very existence. It was responsible for the formation of the Earth, and rendered this planet fit to host living beings, providing the right amount of heat, and this for a long enough span of time. Quite understandably, it has always been a prime target of human curiosity, and more recently one of scientific investigation. During the last century, it was realized that the Sun is a star like billions of others; we learned since that it draws its energy from the nuclear fusion of hydrogen, and we are now able to estimate its age and life expectancy.

The 14 papers in this collection discuss recent progress in areas such as mixing in stellar interiors, redistribution and loss of angular momentum, emphasizing in particular the effects of turbulence. An introductory review by E. Schatzman, to whom this volume is dedicated, is followed by three sections: observational facts (surface abundances, stellar rotation, loss of mass and angular momentum, etc.), physical knowledge (mass transport and mixing by waves, turbulent transport, fast dynamo action, etc.), and the interpretation of observations.

The aim of this Advanced Study Institute was to give an account on the most recent results obtained in solar research. Bucharest was chosen to host it, because the capital city of Romania was located right in the middle of the totality path of the last eclipse of the millennium, on 11th August 1999; furthermore the phenomenon was close to reach there its longest duration: 2m 23s. Such a total eclipse is not only a very spectacular event which draws the crowds: to astronomers, solar eclipses still offer the best conditions for observing the lower part of the corona. The Sun plays a crucial role in our very existence. It was responsible for the formation of the Earth, and rendered this planet fit to host living beings, providing the right amount of heat, and this for a long enough span of time. Quite understandably, it has always been a prime target of human curiosity, and more recently one of scientific investigation. During the last century, it was realized that the Sun is a star like billions of others; we learned since that it draws its energy from the nuclear fusion of hydrogen, and we are now able to estimate its age and life expectancy.