This book is a scientific and evidence based description of the findings of original research work, performed on men, to investigate the effects of a mild increase (+2 °C) in testicular and epididymal temperature on sperm chromatin integrity. For the first time it is reported that a mild increase in testicular and epididymal temperature largely impairs sperm chromatin integrity before any drop in sperm count suggesting that heat stress first affects quality of the gamete and the quantity later. This may have clinical implications in male infertility, repeated miscarriages as well as assisted reproductive technologies. The book beautifully reviews the male reproductive physiology and the data published on the subject during past several decades. The manuscript written in modern style will also help residents and the doctoral students in writing their dissertations.