A dramatic reversal of gender inequality in education occurred when women reached parity with men in college graduation rates around 1982 and surpassed men since then. While scholars have documented this remarkable turnaround in the gender gap in college completion, few studies have offered explanations for why this reversal occurred or why women currently earn a larger percentage of bachelor's degrees than men. The focus of my dissertation is on illuminating the mechanisms of the contemporary gender gap in college completion that favors women. To more completely answer this question, I also examine gender differentials in the college experience that may ultimately affect graduation, including selection of college major and attendance patterns. In order to examine the effects of prior life experiences on college major, attendance, and graduation, I approach these questions through the lens of the life course paradigm and analyze data from the National Education Longitudinal Study of 1988. I find that academic performance and behavior in high school and college are critical factors in shaping men's more disrupted attendance patterns and lower likelihood of graduation relative to women. College experiences, particularly attendance patterns, social integration, and academic performance, do not merely mediate the effects of background characteristics and prior life course events on the likelihood of graduation but are independently consequential for the gender gap in graduation. Although I find that women's lower interest and self-confidence in math partially account for the overrepresentation of men in engineering and related fields, I do not find support for other leading explanations for gender segregation in college major.