Male factors are implicated in as many as 25% of couples with infertility. Assisted reproductive technology (ART) techniques such as intracytoplasmic sperm injection (ICSI) have revolutionised the treatment of infertility and allowed men with severe oligozoospermia, and many with azoospermia, to father their own children. The aetiology of male factor infertility is broadly divided into genetic and acquired causes. Varicoceles are possibly associated with impaired testicular function and infertility. Treatment with certain drugs or exposure to radiation or chemicals can affect actively dividing germ cells causing defective spermatogenesis, and this may be temporary or permanent. Both partners must always be involved in the investigation and management of infertility. Semen analysis is one of the fundamental investigations of the infertile couple irrespective of whether the man has previously fathered children or not. ICSI has become the gold standard treatment for male factor infertility.