One of the biggest concerns educational institutions face is helping teachers fit into and adjust to the dynamics of the ever-changing teaching environment. What often remains a mystery is how the identity trajectories of mid-career teachers have contributed to their longevity in the field. Also important today is why teachers might choose to leave the field after achieving the milestone of becoming a mid-career teacher. This paper reports on a qualitative study looking at the dynamics of mid-career English as a second language (ESL) teacher trajectories in the intensive English program environment. The framework for the study is based on four characteristics common among current teacher professional identity studies identified by Beijaard, Meijer, and Verloop (2004). This framework assumes that teacher professional identity is dynamic, involves individuals with multiple social and professional roles interacting within a shared context to increase individual and collective agency. In this study, mid-career teachers currently teaching in intensive English programs (IEPs) who have made transitions from at least one context to another were interviewed to investigate common themes in their experiences. Results show that while individual factors are important in the development of a professional identity, the most important factors seem to be related to the administrative support systems in place and student performance as connected to teaching 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.]