Engineering education research can benefit from comprehensive tools for assessing student self-concept and its relationship to identity development. This research addresses this gap by introducing a novel framework for evaluating engineering self-concept and exploring its influence on identity status transitions among first-year students. Key sub-constructs of engineering self-concept were identified through an extensive literature review, distinguishing it from self-efficacy. A new survey instrument for assessing engineering self-concept was developed, pre-tested with subject matter experts and was statistically validated. Confirmatory factor analysis was used to validate the theoretical framework and to examine the relationship between engineering self-concept and self-efficacy. After establishing the framework for engineering self-concept, measures of identity status were integrated into the analysis to investigate identity status transitions in first-year engineering undergraduates. Significant transitions were observed amongst cohorts of students. A qualitative interview methodology provided insights into specific transition patterns that were observed. Interpretations further explored connections between engineering self-concept and various identity statuses. Findings contribute to the field of engineering education by providing a validated tool for assessing engineering self-concept and insights into the relationship between self-concept and identity development. Implications extend to structural adaptations to enhance undergraduate student identity development, improve student performance and commitment to engineering, and inform educational strategies for increasing retention and persistence in engineering programs. This work lays the foundation for future research aimed at supporting the holistic development of engineering students during their critical first year. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]