To better understand teacher retention, the thrust of the study was to investigate the relationships among principal support, teacher efficacy, collective efficacy and practicing teachers' commitment to the profession. This study was designed to test the mediating role of teacher and collective efficacy beliefs on teacher commitment facilitating three mediation models. Data come from 260 public school teachers in the Washington DC area, aged between 20 and 69, who completed three questionnaires through which a predictive and mediation model of teacher commitment was tested. Teacher efficacy and collective efficacy beliefs were hypothesized to mediate the relations between the principal support and teachers' commitment to teaching profession. Mediation regression modelling was used to test and validate these three models across the sample of K-12 teachers. Teacher collective efficacy beliefs were found to be partially mediated the relationship between principal support and teacher commitment to teaching profession whereas general teacher efficacy and personal teacher efficacy did not mediate the relationship between principal support and teachers' commitment to the profession of teaching. The measures in this study can be used to guide professional development and measure how successful attempts are to increase teacher commitment.