Major choice matters for both individuals' welfare and the overall economy. A large body of studies in various countries has documented the determinants of college major choices, such as individual background characteristics, expected earnings and ability sorting, structural barriers in K-12 education, peer and family influences and expectations, and supply-side factors (Kanny et al., 2014; Patnaik et al., 2020). This three-chapter dissertation contributes to the literature on college major choices by providing new evidence on the role of factors from both the investment side (student demand) and the supply side (college major reforms) in the college major choices of students in China. In the first paper, "Do Women Hold Traditional Gender Role Beliefs More/Less Likely to Choose STEM Majors in China?", I investigate the role of gender role beliefs in female and male students' college major choices. Women continue to be underrepresented in most STEM-related fields in both higher education and the labor market. The study extends the existing literature by exploring the role of individual gender-related beliefs in college major choices. Using representative college student survey data, I find that female students are substantially underrepresented in most STEM majors. Gender role belief can be one potential underlying psychological factor that explains the gender disparity in STEM major choices. Female students with more traditional gender role beliefs are more likely to choose STEM. The association between the traditional gender role beliefs and STEM major choices for females is predominantly concentrated in the non-advantaged STEM majors and STEM majors at non-selective universities. The pattern exists for students who originate from more advanced household statuses and regions, but not for high-achieving students. Female students entering the STEM domain experienced internalized sexism by assimilating the gendered social norms and endorsing the male privilege in this field. In the second paper, "The Impacts of College Major Reforms on Student Composition in China," I examine the effects of college major reforms on student composition within college-majors. In the context of the Chinese meta-major reform, this paper provides one of the first empirical evidence on the consequences of a transition from college-major to college-then-major choice mechanism. Using administrative data on college admissions over 18 years, I study the impacts of the staggered adoption of the reform across institutions on student composition. I do not find aggregately statistically significant effects of the meta-major reform on the distribution of ability and demographic characteristics of students by college-majors. The result is robust to using alternative measurements, samples, models, and estimators. However, the aggregate null effects are masked by the heterogeneity across institutions and majors. The impact of increasing admission scores is predominantly concentrated in non-elite institutions and non-advantaged STEM majors. The reform also alters the student profile in terms of ethnicity and place of origin at the most prestigious institutions. The third paper, "College-Major Choice to College-then-Major Choice Reform: Experimental Evidence on Student College Major Choice Behavior" - studies students' responses to various types of information on meta-major reform. One of the most important mechanism design policies in college admissions is for students to choose a college major sequentially (college-then-major choice) or jointly (college-major choice). However, how students behaviorally respond to these policies is unclear. In the context of the Chinese meta-major reforms, the paper provides one of the first experimental evidence on the heterogeneous impacts of a transition from college-major to college-then-major choice on students' willingness to apply, with a special focus on the role of information. In a randomized informational experiment with a nationwide sample of high school graduates, the results show that providing information on the benefits of a meta-major significantly increased students' willingness to apply; however, information about specific majors and assignment mechanisms has insignificant impacts. The information mostly affects the preference of students who come from disadvantaged backgrounds, lack accurate information or clear major preferences, or are risk-loving. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]