This book offers a highly informative guide to treating unexplained infertility and recurrent miscarriage (RM). In particular, it provides detailed treatment strategies for infertility or RM derived from uterine circumstance such as chronic endometritis and perturbation of endometrial decidualization, as well as maternal immunological rejection of an embryo as semi-allograft.Unexplained infertility refers to those types that cannot be detected by the general screening test. The causes are sometimes detected in the course of treatment with assisted reproductive technology including IVF. However, some unexplained infertility is intractable even after intracytoplasmic sperm injection or repeated implantation of morphologically suitable embryos. Patients with unexplained RM also have a high likelihood of undetectable risk factors of miscarriage.