Spermatozoa is the basic human male germ cell. This gametocyte plays an important role in fertilization. In the past five years, new improvements in diagnosis have allowed us to assess male fertility potential with a new perspective studying with demonstrated role in sperm physiology. Furthermore, it is demonstrated that infertile men have high levels of sperm DNA damages and a small percentage of spermatozoa from fertile men also possess detectable levels of DNA damage. This book examines several of the factors that may be involved in sperm chromatin and DNA anomalies, including intra and extra testicular factors. Furthermore, sperm capacitation is a complex physiological process that involves biochemical, biophysical, molecular and metabolic modifications of all sperm domains. Some important events related to the capacitation process of sperm is examined as well. The biological role of the proteasome during sperm capacitation and the acrosome reaction and its relationship with protein phosphorylation and dephosphorylation during these processes is explored as well. Other chapters in this book highlight the pivotal role of transmission electron microscopy (TEM) analysis in the diagnosis of human sperm pathologies, the barrier methods currently available to men for regulating their fertility, a discussion of the current understanding of gene transfer to the testis, a new perspectives for the study of mycoplasmal and chlamydial infections of human spermatozoa and a discussion of the present current knowledge on the mechanisms, molecules and cell signaling involved in sperm activating ability.