This book is composed of chapters prepared by invited speakers of the XIVth North American Testis Workshop held in Baltimore Maryland February 19 to 22 1997. The book reflects the desire of the Testis Workshop Scientific Commit- tee for a program addressing a broad array of current research focused on the germ cell from its development through its death. Consequently the research of those who have contributed chapters to this book addresses or can be applied to the hormonal and molecular regulation of spermatogonial cell development and nmc- tion (Nishimune Orth Russell Dym) meiosis (Bickel Wolgemuth Handel Trasler) spermatogenesis (Sassone-Corsi Habener Braun) cell death and aging (Campisi Chen Knudson Swerdloff) and toxicant effects on spermatogenesis (Sharpe Keice Robaire Meistrich). In their preface to the proceedings of the 1988 Testis Workshop Drs. Larry Ewing and Bernard Robaire noted that the first published description of semi- niferous tubules in the testis was in 1668 by C. Aubry and that the exciting papers in these proceedings [of the 1988 Workshop] emphasize the significant progress that has been made since the mid-17th century in understanding testis and function. It is quite clear that current research is proceeding at a breathtaking pace with enormous strides having been made even since the XIIIth Workshop in 1995. If the XIVth Workshop succeeded and this book succeeds in convey- ing this excitement in our field (which of course was our intent) credit belongs to the creativity of the Scientific Committee whose members were William J.