Teacher well-being has become an increasingly critical area of research, particularly considering the significant challenges faced by educators in recent years. Studies have shown that the COVID-19 pandemic exacerbated pre-existing demands, responsibilities, and stress, contributing to rising burnout and teachers' intentions to leave the profession (Matthews et al., 2022; Pressley et al., 2024). Addressing teacher well-being has become essential not only for supporting educators' mental health but also for ensuring teacher retention and the sustainability of the education system. This dissertation explores teacher well-being through two studies. Chapter 1 is a systematic review of 20 U.S.-based empirical studies published between April 2020 and April 2024, focusing on regular K–12 teachers across remote, hybrid, and in-person instruction during the COVID-19 pandemic. The review addresses two key research questions: (1) What factors influenced teachers' well-being during the COVID-19 pandemic in the United States, and how did these factors vary based on demographic characteristics? (2) What were the effects of COVID-19 on teachers' personal and professional well-being in the United States? A thematic analysis identified five key factors shaping teacher well-being: workload and role expansion, leadership and administrative support, relationships and collaboration, teaching environment, and systemic factors such as equity and demographics. Additionally, three outcome themes emerged: emotional and mental health outcomes, coping strategies and support systems, and professional identity and satisfaction. These findings provide insights into the challenges educators faced during the pandemic and offer recommendations for developing targeted interventions to support teacher well-being in future crises. Chapter 2 shifts the focus from the pandemic to a broader examination of teacher stress by exploring how student misbehavior, teacher-student relationship quality, and teacher self-efficacy relate to teacher stress. Using data from 375 U.S. elementary public school teachers, the study employed multiple regression analyses to examine whether teacher-student relationships (TSR) closeness, TSR conflict, and teacher self-efficacy in managing student misbehavior moderated the relationship between student misbehavior and teacher stress. The results showed a direct positive association between student misbehavior and teacher stress, with high TSR closeness and low TSR conflict buffering this relationship. TSR closeness offered little protection at high misbehavior levels, while TSR conflict continued to buffer teacher stress, though more strongly at lower levels. Surprisingly, teacher self-efficacy did not moderate this relationship significantly. These findings contribute to the broader understanding of teacher stress, showing how classroom dynamics can mitigate the negative effects of student misbehavior, beyond the context of the COVID-19 pandemic.