This volume is the proceedings of the International Taurine Symposium 1999: Expanding the Circle, an official Satellite Symposium of the 17th Biennial Meeting of the International Society for Neurochemistry, held on August 3-8, 1999, in Siena, Italy. Taurine, which is a naturally occurring compound, protects the cell against a variety of harmful insults, and the compound may be vital for the normal function and survival of cells and tissues. These aspects, together with the potential value of taurine in enhancing normal function and protecting against age-related diseases, will be highlighted in this volume by international aspects in this important and rapidly developing area.