Embryo reduction (ER) may be indicated in a number of situations in fetal medicine. This chapter summarizes the available evidence on ER and discusses the impact of several factors which might influence results. It talks about the techniques and outcomes of selective ER in dichorionic twin pregnancies. Selective ER in twins may be indicated for elective reasons, because of the parents' desires to reduce the number of embryos and/or improve pregnancy outcome, the presence of an increased fetal or maternal risk, or the presence of a discordant anomaly. Elective ER is normally performed as early as possible in pregnancy. Embryo reduction can be performed transvaginally or transabdominally. The outcome of dichorionic twins electively reduced to singletons in the first trimester is clearly worse than in singleton pregnancies; they deliver earlier (roughly 37.5-38 weeks) and have an increased rate of early pre-term delivery (2.5-7.5%).