With increasing embeddedness of information technologies (IT) in organizational processes, and services, individuals' long-term IT use has become instrumental to business success. At the same time, IS research has illustrated that under-utilization by end-users often prevents organizations from realizing expected benefits from their technology investments. Because individual use is the critical link between technology investments and enhanced organizational performance through IT, in recent years, information systems researchers have begun to focus attention on the post-adoption phases of technology assimilation. The overarching goal of this relatively new research stream is to understand factors that influence individuals' attempts to use IT to their fullest potential in the work setting. To advance research on post-adoption IT use, this three essay dissertation develops, operationalizes, and tests the new concept of "information technology (IT) identity"--defined as, "the set of meanings an individual attaches to the self in relation to IT"--as a "product" of individuals' personal histories of interacting with IT, as well as a force that shapes their thinking and guides their IT use behaviors. The first essay builds the core concept through exploring whether young people's individual self-concepts are tied to their interactions with mobile phones. The second essay draws on a rich repertoire of literature to formally theorize the domain and dimensions of IT identity, as well as its nomological net. By examining the processes by which IT identity is constructed and maintained, this essay offers IS researchers a new theoretical lens for examining individuals' long-term IT use. The third essay develops an operational definition of IT identity and empirically tests the conditions under which the construct is a more or less salient predictor of individuals' post-usage intentions and continued IT use than existing IS constructs. The results presented help delimit a role for IT identity in bridging the gap between current models of use and models that explain long term and richer IT use behaviors. Extending understanding of why and how individuals use IT in the long term may help provide a basis for designing managerial interventions that promote organizational assimilation of IT. Thus, by proposing and operationalizing IT identity as a core construct in explaining individual IT use, this research has the potential to advance theory and contribute to practice. [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.]