This paper, prepared as a Background Paper for the Institute of Medicine's Committee on Unintended Pregnancy, discusses economic perspectives on fertility and unintended pregnancy. The paper proceeds in two parts. The first part of the paper presents a theoretical discussion of a rational choice/economic theory perspective on the decision to have a child. The insights of that discussion are then used to consider the interpretation of the phrase "unintended pregnancy" and some recent work by economists analyzing individual reports of the intendedness of pregnancy. The second part of the paper reviews the literature on the effects on fertility of payments to parents and the total cost of contraception/abortion.