**1. Introduction**

The search for source of infection and infertility has been an active area of study for many years. Because the source of infection is complex, we divided the source of infection into three groups: virus, such as mumps virus, hepatitis B virus, human papillomavirus, herpes simplex virus, and human immunodeficiency virus; bacteria, such as *Chlamydia trachomatis* and *Helicobacter pylori*; and parasite, such as *Toxoplasma gondii*. First, we review the association of these infections and infertility. Because genetic influence may play important roles in regu‐ lating the infection in fertility, we also discuss the genetic effects on infertility, mainly the gene polymorphisms influencing infection and infertility in the following sections.
