The past few years have brought an influx of new information into the field of male reproduction. Several laboratories have been able to apply the genomics approach to gene expression in the male, revealing previously unknown patterns of gene expression and gene products that were localized in male reproductive tract tissues and cells for the first time. These discoveries paved the way for the next wave, an opportunity to analyze male reproductive biology and the processes by which sperm are formed in the seminiferous tubule and androgen is synthesized in the interstitium of the testis. The different levels of organization in the testis, including the stages of spermatogenesis, enzymatic steps of steroidogenesis, and the intracellular signaling pathways of hormones, are now more amenable to study and selection of potential targets for drug development. This volume capitalizes on these developments with a collection of reports that is uniquely suited to stimulate research and development ideas.