Written as a set of lecturers and tutorial reviews this book has emerged from a summer school devoted to the gravitational aspects of the sun and their geophysical consequences. The gravitational distortions of the sun can be used to gain some knowledge of the sun's interior and surface phenomena but also influences the sun's irradience and thus ultimately the earth's climate. Last but not least, these small distortions constitute a formidable challenge to solar astrometry and the last part of the book describes the observational difficulties in defining unequivocally the solar diameter.