This qualitative grounded theory study created a theory, including a definition, of overcommitment in undergraduate students at a four-year public institution. Although overcommitment has been studied for decades, the concept of overcommitment in undergraduate students has not been thoroughly explored. Undergraduate students can overcommit in a variety of domains, including academics and co-curricular activities. The central research question for this study is, how do full-time undergraduate students define overcommitment? Overcommitment has been tied to several mental and physical health issues. With student mental health issues on the rise on college campuses, it is imperative that overcommitment in undergraduate students be explored and defined. This study included 21 undergraduate college student participants, who met the following criteria: (1) enrolled as a full-time undergraduate student; (2) identified by a higher education professional as committed or overcommitted. Data was collected through a demographic survey, as well as, 60-minute semi-structured interviews on Zoom with each student participant. Data were analyzed through three rounds of coding: (1) open coding, (2) axial coding, and (3) selective coding. Three major themes emerged from the analysis of the undergraduate students' overcommitment definitions: doing too much, lack of basic self-care, and detriments to mental and physical health. After synthesis, it was determined that undergraduate students define overcommitment as "taking on too many commitments to the overall detriment of mental and physical health, due to the lack of basic self-care." The interview codes were ultimately developed into themes to create the theory of undergraduate student overcommitment as evidenced in the Undergraduate Student Overcommitment Model and answer the remaining research sub-questions about identification, challenges, benefits, and social supports and strategies. The theory explains undergraduate students' rationale for overcommitting and has six levels: self, family, peers, school, future dreams and goals, and society. After careful data analysis, it was determined that how undergraduate students define overcommitment and how they live out their overcommitment is different -- their definition does not encapsulate the full picture of undergraduate student overcommitment. Based on extensive research through this grounded theory study, I offer a new definition of undergraduate college student overcommitment: A motivation cycle fueled by a high need of approval from self and others, that involves exerting excessive effort through numerous commitments, in hopes of obtaining delayed rewards. This study is beneficial for students, parents/families, and higher education faculty and staff, especially student life and student leadership personnel, to learn about overcommitment. Recommendations include students and parents/families learning about undergraduate student overcommitment, attending workshops and trainings, and having real and realistic conversations about undergraduate student overcommitment. Recommendations for higher education professionals include intentionally selecting a variety of students for various leadership roles, changing language about what graduate/professional schools are "looking for" in regards to admission, implementing overcommitment workshops, encouraging mental health services, and expanding mentor experiences. [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.]