Although abortion became legal four decades ago, Americans remain staunchly divided over its acceptability. While researchers have been interested in the factors shaping abortion attitudes, there are almost no reviews of this work. We examine the factors shaping Americans' abortion attitudes and assess the state of published peer-reviewed articles in this area over the last 15 years. Using a mixed-methods systematic review, we analyze and critique the findings from 116 journal articles that have examined attitudes about abortion between 2001 and 2016. Among the many predictors and outcomes examined, we show that religion is by far the most utilized statistically significant independent variable, followed by education and income/employment. In addition to examining the factors that shape attitudes, we provide insight into the characteristics of this published work. We offer several suggestions for improving research on this important topic, including a better utilization of social science theory, examining the attitudes of teens, increasing the use of mixed-methods studies, and drawing on longitudinal data and analyses that consider the influence of the larger context for shaping attitudes. Although abortion became legal 40 years ago, Americans have remained staunchly divided on whether or not women should be allowed to obtain them and the circumstances and point in their pregnancies under which they are acceptable. Public opinion data from Gallup shows that in 1976, 54 percent of Americans said that abortion should be legal under only certain circumstances (Gallup 2018). Since then, support has only minimally increased with 50 percent of Americans today reporting that abortion should not be legal (Gallup 2018). The minimal change in abortion attitudes is a sharp departure from the massive increases in support for other issues, like legalizing cannabis and same-sex marriage, which at one time would have also been viewed as highly deviant (Adamczyk 2017; Felson, Adamczyk, and Thomas 2019). In contrast to attitudes about abortion, between 1988 and 2014 support for both cannabis and same-sex marriage legislation increased substantially (Schnabel and Sevell 2017).