This chapter provides the background information of the recurrent pregnancy loss (RPL), and its diagnosis and treatment method. The medical literature is replete with definitions ranging from three or more consecutive pregnancy losses before 22 weeks of gestation to simply two or more clinical miscarriages, the definition used by the American Society for Reproductive Medicine. Despite a wide range of prevalence estimates throughout the RPL literature, RPL is generally estimated to occur in approximately 1 to 5% of women trying to conceive. The diagnostic evaluation of RPL includes: serum karyotype analyses on both parents, cytogenetic analysis of abortus tissue, uterine assessment, antiphospholipid antibodies, and endocrine studies. The rationale for assisted reproductive technologies like intrauterine insemination and IVF includes the possible correction of potential endocrine, immunologic and sperm factors. Preimplantation genetic screening of embryos for aneuploidy allows selection of euploidembryos for transfer.