Unexplained infertility refers to the inability to conceive after one year despite routine investigations showing no abnormalities. While the causes are uncertain, treatments aim to increase monthly pregnancy rates and include expectant management, clomiphene citrate, gonadotropins, IUI, IVF, and lifestyle changes. Couples with unexplained infertility have higher risks of obstetric complications and should follow a progressive treatment plan based on factors like duration of infertility and age.