This dissertation formulates and tests a theory about factors affecting postsecondary education (PSE) enrollment. Enrollment outcome is hypothesized to be affected by academic preparation, finances, and social capital factors. Special focus is placed on relevant social capital constructs: access to information, attainment norms, and support; social network effects are also analyzed. Data come from the National Education Longitudinal Study-8th grade 1988-cohort (NELS:88). The main analytical method used is the multinomial logit model (MNLM), which is a proper analytical technique for estimating choice models in which the outcome variable is categorical or only partially ordered. The MNLM estimates simultaneously binary logits for all possible comparisons among the outcome categories, allowing estimation of different effects of predictors in each outcome category. MNLM analyses confirm that dynamics affecting enrollment in postsecondary education vary for two-year and four-year institutions. Variables measuring the four social capital constructs—attainment norms enforcement, access to information, support, and social networks—were significant for both enrollment in two-year and four-year institutions. The MNLM results indicate that social networks and peers greatly impact enrollment in two-year institutions. Largest effects on enrollment in two-year institutions are from volunteering, feeling involved in the neighborhood, friends to attend college (two-year or four-year), and family income. Results indicate that all social capital constructs—information, attainment norms, and support—as well as social networks variables effect enrollment in a four-year institution. Both parents' and students' sources of information on financial aid show positive effects on enrollment in a four-year institution as do variables measuring attainment norms and high school help in college application process. Variables measuring community involvement and social networks are among the strongest predictors of enrollment in both two-year and four-year institutions. PSE institutions may use these results for planning and implementing informational outreach and enrollment management strategies. The model has potential for informing public policies aimed at increasing PSE enrollment rates for disadvantaged students.