This study addresses a gap in language learning regarding the relationship of teacher well-being with different aspects of instruction, namely, teaching practices and student learning (Turner & Thielking, 2019). Specifically, the study explores the link between second language (L2) teachers' well-being levels, the L2 teachers' instructional practices and the relationship between instructional practices and a precursor of learning, L2 students' engagement. The study was conducted with Colombian teachers of English as a foreign language who work in secondary schools and have different years of teaching experience and academic degrees (N = 203). The study also included students from 6th to 11th grade enrolled in English classes in the 2021 school year (N = 1544). The data were collected in March, 2021. In this cross-sectional study the research questions sought to identify the well-being levels of L2 teachers, the factors that make up well-being in the sample, the relationship between L2 teachers' well-being and L2 instructional practices, and finally whether these instructional practices served a mediating role between L2 teachers' well-being and the levels of L2 learners' classroom engagement reported by the secondary students. The PERMA-Profiler measured L2 teachers' well-being levels. The frequency of occurrence of the L2 teachers' instructional practices teachers was identified through a 24-item self-report survey, and L2 learner's classroom engagement was measured through a 14-item survey. EFA & CFA analyses showed that one factor made up well-being in the sample and that the items could be categorized in the same dimensions identified in previous studies (Butler & Kern, 2016). Data also showed that Colombian L2 teachers had normal functioning levels of well-being (M = 7.7) according to Kern's (2020) categorization. Demographic factors like age, experience and academic degree did not seem to affect or interact with teacher well-being. In addition to this, regression analyses indicated that the well-being levels of L2 teachers had a significant relationship with their instructional practices (p < 0.001). Finally, two competing models, one including direct pathways between teacher well-being and learner engagement and the other including only mediation pathways were compared. A Sobel test conducted to examine the mediation suggested that the model including only mediation was more suitable to explain the data. It also showed that L2 teacher well-being and L2 student engagement were mediated by instructional practices, and that the relationship was significant (p < 0.01). It can be concluded that L2 teacher well-being levels are associated to the use of effective L2 instructional practices, which, in turn, are linked to the L2 students' classroom engagement. The study contributes to a better understanding of the construct of L2 teacher well-being as it shows that teacher well-being interacts with other aspects of teaching such as instruction. This study is the first one measuring L2 teachers' well-being in Colombia and it makes a theoretical and methodological contributions by linking the data of L2 teachers and students. The study has pedagogical implications for teacher education and professional development programs that support the well-being of teachers (Oncevska & Mercer, 2019). [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]