The completion of the human genome and technological advances developed by the Human Genome Project have dramatically changed our understanding of the mechanisms underlying the development and differentiation of male germ cells, and our ability to investigate such mechanisms. This book is a timely document of advances made in the field of male gonad and germ cell research in the postgenomic era. The coverage includes the role of Y chromosome genes in male reproduction, gene expression in spermatogonial stem cells and male germ cells, and the regulation of germ cell genes in reproduction and in germ cell tumors.