In this survey article, I review evidence regarding the prevalence of unintended pregnancy, its root causes and consequences, the effects of various policies designed to curb its incidence, and the political and legal contexts within which those policies are debated.  I begin by synthesizing the most recent available data on the incidence of unintended pregnancy.  I show that, over the last decade and a half, unintended pregnancy rates have dropped substantially among teens but have increased somewhat among older women.  The net result of these two trends has been a modest increase in the overall rate of unintended pregnancy.  These trends have important implications for children, for families, and for society at large, as unintended pregnancy is associated with outcomes ranging from high school dropout and child poverty to juvenile delinquency and abortion.  I review the extensive academic literature on the causes of unintended pregnancy and the likely effects of policies aimed at reducing its incidence.  With respect to the first of these two topics, there is evidence to suggest that some individuals lack the motivation to avoid unintended pregnancy; that others possess the necessary motivation but have little understanding of how to follow through on their intentions; and that still others are armed with the right information and the desire to put it to good use but have limited access to the most effective forms of contraception.  There is also a body of research showing that public policy can affect each of these root causes via interventions such as media campaigns discouraging unsafe sex, comprehensive teen pregnancy prevention programs, and expansions in government subsidies for contraceptive services.  New evidence further suggests that such programs may generate substantial taxpayer savings.   In recent years, some members of the policymaking community have invested in programs of this sort while others have sought to reduce or eliminate existing sources of funding for them.  I conclude that evidence-based pregnancy prevention programs have the potential to produce a variety of benefits – improved life prospects for women and children, lower rates of abortion and single parenthood, and reduced government spending – that ought to hold appeal for policymakers of all political stripes.