Infertility is defined as the inability to achieve a pregnancy after 12 months of unprotected sexual intercourse, affecting millions globally, with varying causes between male and female reproductive systems. Causes of infertility can be categorized into primary, where a couple has never conceived, and secondary, where they have previously conceived but face difficulties in subsequent attempts. Diagnosis involves detailed medical history, physical exams, and specific investigations such as semen analysis and hormonal assessments to determine the underlying factors contributing to infertility.