This article covers the rapidly advancing field of preimplantation genetic diagnosis (PGD), the molecular genetic analysis of cells taken from embryos formed through in vitro fertilization (IVF). The article focuses on current practices in patient management, relevant IVF and PGD procedures, molecular methods used in the genetic analysis, and technical difficulties that can affect test results. It discusses the growing list of indications for PGD including chromosomal disorders, monogenic disorders and human leukocyte antigen typing typing of embryos. The article also examines some of the emerging technologies being introduced into PGD.