At many universities, more than half of students change majors at least once and a large fraction of these students change majors multiple times. The potential causes and effects of these very common behaviors are relatively understudied. This dissertation explores the college major decision-making process, both for initial and subsequent major choices, and analyzes the associations between major choice behaviors and student outcomes such as time to degree and probability of graduation. This was done via a descriptive quantitative analysis of nationally representative data along with a mixed methods case study at an Ohio public university. This case study included interviews and focus groups with major deciding students, major switchers, and academic advisors along with a descriptive quantitative analysis of data from university graduates. The results suggest that entering college undecided has no cost in terms of a reduction of probability of graduation or little cost in terms of extending time to degree if a major is declared prior to sophomore year. Major switching is associated with extended time to degree, but the timing at which the final major decision is made drives the extent of this cost. There is some evidence that major switching may raise the probability of graduation. This may be because poor academic performance is a primary driver of major switches, a finding well supported with both qualitative and quantitative evidence. University administrators and other policy makers can use findings from this work to help design programs and interventions that will help major decision-making students find the right major for them more quickly and avoid costly major selection behaviors. Exploratory programs with intensive advising for undeclared freshmen are a good idea and there is a good argument for extending these services to declared freshmen as well. Requiring a visit to an academic advisor prior to a major switch can help students avoid particularly costly switches. Career or field activities in a major area or academic performance in a key gatekeeper course like science or math make students decisive about a major and should be encouraged to be undertaken as early as possible. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]