Infertility is a common problem affecting one couple in six. It can be defined as the incapacity to fulfill pregnancy after reasonable time of sexual intercourse with no contraceptive measures taken. The evidence for changes in the prevalence of infertility is difficult to establish. This increase could be due to at least four factors: delayed childbearing, alterations in semen quality due to habits such as cigarette smoking and alcohol, changes in sexual behaviour and eliminations of most taboos. The study of infertile couple has always been focussed on different factors: ovulatory factor (present in about 20% of couples), utero-tubal peritoneal factor (present in ~30% of couples), semen migration factor (10% of cases) and male factor (30% of couples). Around 40% of all infertile couples exhibit a combination of factors and about 15% of couples may not display any objective alteration leading to a definite diagnosis. During the past two decades there have been three important changes in infertility practice. First, the introduction of assisted reproduction technologies has provided an opportunity to study basic reproductive processes. Second, societal changes have occurred such as the increase in the proportion of women over 35 years old seeking pregnancy. This fact is due to a later age for marriage and postponement of pregnancy. Third, the development of molecular biology and genetics has become very important for the study, diagnosis and assessment of couples, many of them considered until now as "unexplained infertile couples".