In this paper we examine the level and determinants of entering college students' plans to major in engineering. While the overall level of interest in engineering has fluctuated between 1971 and 2011, a very large gender gap in freshman interest remains. We find that the percent of first-year women who plan to major in engineering is roughly the same today as in the early 1980s. We estimated the impact of predictor variables for five time points: 1976, 1986, 1996, 2006 and 2011. Independent variables were grouped into eight categories: personal inputs, background characteristics, learning experiences, self-efficacy, outcome expectations, interests, contextual influences, and choice goals. We present the findings in terms of those variables that have a consistent effect on the gender gap over time, and those whose effects vary over time.