Male infertility is a serious ongoing problem. Many reasons are synchronized in increasing the male infertility including pesticide exposure. Cypermethrin is a commonly used pesticide in agriculture that is known to affect human health. This book mainly focuses on giving an understanding the toxic effects of cypermethrin on male reproduction along with the molecular mechanisms underlying the reproductive toxicity. In addition, the factors responsible for compromised steriodogensis/spermatogenesis in adult male rats were also addressed. In general, testosterone replacement therapy (TRT) is used to treat male reproductive disorders especially in those suffering from insufficient testosterone levels. In view of this, the authors made an attempt to throw light on the hormonal regulation, spermatogenesis, steroidogenesis, role of StAR protein and anti androgenic activity of cypermethrin and the protective effect of testosterone against cypermethrin induced toxicity.