Background: The charter school movement relies on teachers as critical components. Teacher commitment is an important aspect of teachers' lives, because it is an internal force for teachers to grow as professionals. It is also considered one of the crucial factors in influencing various educational outcomes, including teacher effectiveness, teacher retention, and student learning. However, no empirical studies have examined teacher commitment in charter schools. Purpose: To address this knowledge gap, this study compares organizational and professional commitment of teachers in charter schools and traditional public schools (TPSs) and explores how these differences are associated with teachers' characteristics, school contextual factors, and working conditions in the two types of schools. Research Design: This study utilizes quantitative analyses of national data from the 2007-2008 School and Staffing Survey. Hierarchical linear models were developed to examine whether teacher commitment differs between charter schools and TPSs; how teacher characteristics, school contextual factors, and teachers' perceptions of working conditions contribute to the difference; and finally, whether these variables differentially influence teacher commitment in charter schools and TPSs. Conclusions: On average, teachers in charter schools experienced lower levels of organizational commitment than teachers in TPSs, but similar levels of professional commitment. Teacher working conditions explained a large amount of the variance in between-school teacher commitment, suggesting that improving principal leadership, increasing opportunities for professional development, and alleviating teachers' workload would be effective ways to promote teacher commitment in charter schools.