This dissertation illustrates how admission policies shape access to postsecondary education. Evidence comes from two sectors, each with a distinct type of admission system: highly selective institutions that practice holistic admission (chapters 2 and 3) and less selective public four-year colleges that use admission thresholds (chapter 4). The first two analyses draw on admission data from academically selective universities included in the National Study of College Experience. The third analysis relies on admission, enrollment, and graduation data from a large public urban university system. In chapter 2 I show that selective institutions practice place-based affirmative action, giving students from low-income areas a boost in admission relative to comparable applicants from higher-income areas. This policy rewards applicants who faced educational disadvantage in their neighborhood and school environments and present a credible candidacy nonetheless. In chapter 3 I explore a potentially unintended consequence of controversial admission policies. Specifically, I test whether admitting a student in a preferred but controversial admission category from a given high school makes admission officers more likely to also admit top-ranked students from the same high school to assert core academic values. There is anecdotal evidence for this so-called "coattails" phenomenon, but I do not find evidence for systematic practice. In chapter 4 I show how an admission policy that initially denies weak students access to four-year public institutions ultimately harms them academically. When marginal students who are denied admission following changes in minimum thresholds are diverted to two-year colleges, they are significantly less likely to complete a bachelor's degree than if they had started at a four-year college. The research is motivated by the fact that access to postsecondary education is greatly unequal. College enrollment is characterized by large income disparities--not only in overall rates, but also in college sector and institutional selectivity. Despite limits to the potential impact of higher education institutions, colleges and universities have flexibility in shaping incoming classes and providing opportunity to a college career and degree through direct and indirect admission policies. [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.]