The decision to major in engineering and the selection of a discipline within engineering are two separate choices. Students who choose an engineering discipline that makes the best use of their skills and abilities, engages their interest, and aligns with their values, are more likely to thrive in the discipline of engineering they choose. However, there is little empirical work examining how students choose their engineering discipline, and therefore a lack of understanding of the disciplinary choice process. This thesis reports on a course of research investigating how and why engineering students choose a discipline of engineering. The first part uses prior literature on career, major, and disciplinary choice to propose a theory of disciplinary choice specific to engineering. The second part reports on two studies carried out with engineering students (N = 978; N = 395 respectively) to identify the factors influencing their choice of discipline. The third part reports on two studies carried out with engineering students (N = 867; N = 395 respectively) using survey data to test the proposed model of disciplinary choice in engineering. Findings from these studies support the proposed theory of disciplinary choice and show that the choice of engineering as a major is distinct from the choice of an engineering discipline for many students. The studies also indicate that students make the choice of discipline based on their perception of how the disciplines match their self-concept which is made up of students' interests, goals, values, and abilities, and their future desires and expectations. Findings imply that students need a better understanding of each engineering discipline to make an informed choice. [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.]