This article describes a validation study using Retrodictive Qualitative Modeling, a framework for conducting research from a dynamic and situated perspective, to establish an empirical foundation for a new phenomenological construct--language teacher immunity. Focus groups (N = 44) conducted with second language (L2) practitioners and teacher educators and a cluster analysis of questionnaire data with a larger sample (N = 293) of K-12 language teachers were used to identify and corroborate typical archetypes across the spectrum of language teacher immunity outcomes. Serial in-depth interviews were then conducted with representative respondents from each archetype (N = 18) to trace developmental trajectories and investigate how these profiles manifested phenomenologically in teachers' motivated thought and instructional practices. Results indicate that teacher immunity is associated with practitioners' psychological, emotional, and cognitive functioning in the social setting of the L2 classroom. These findings contribute to the field's understanding of how language teachers sustain their adaptivity, openness to change, psychological well-being, and their sense of purpose and investment in students' learning. Thus, teacher immunity has the potential to bridge individual and situative concerns in second language teacher education and the psychology of language teaching and learning.