Teaching is a challenging profession sometimes leading to teachers' burnout: a syndrome of emotional exhaustion, depersonalisation, and reduced personal accomplishment. Burnout effects range from psychological, physical, and behavioural symptoms to increased turnover, which affects students and schools. This study identifies levels of and factors causing Lebanese teachers' burnout by eliciting their perspectives about the matter. A multiple-case studies design is used; instruments include interviews, researcher's reflective journal, and questionnaires adapted from the Maslach Burnout Inventory-Educators Survey. Nine teachers who left the profession during the first five years of teaching were interviewed and 92 teachers in service responded to the questionnaire. A cross-case synthesis helped to compare the data between cases in order to discover whether similarities can be found. Triangulation of data is performed through comparing results from each instrument and identifying common categories that are used to address the research questions. Findings show that workload, school environment, coordination/mentoring, classroom environment, and emotional factors are major causes of burnout. This study provided insight on how to identify causes and symptoms of teacher burnout to help prevent the occurrence of the syndrome.