Oxidative stress is an important aetiological factor which leads to sperm DNA damage and infertility. It damages all biomolecules and both mitochondrial and nuclear DNA and adversely affects sperm membrane fluidity and motility. This acts like a biological safeguard however use of such sperm for ART/ICSI can lead to pre and post implantation losses, major and minor congenital malformations and even childhood cancer. Thus it is important to know the causes of oxidative stress and how the levels of free radicals be maintained at physiological levels when they are beneficial for normal function. It is also important to develop techniques to identity cases with high free radical levels and also adopt certain life style measures which can minimise oxidative stress and improve male reproductive health.