A school's performance over time is shaped by its ability to retain strong teachers. Research has identified multiple predictors associated with teacher retention; however, few studies have investigated the association between person-organization and person-group fit and teacher retention. The purpose of this study is to investigate the association between three measures of fit and teacher retention. The authors utilized a longitudinal data set that included 132 early career teachers (ECTs) with social network data from their mentors and colleagues. Data analysis identified that person-organization professional fit was positively associated with ECTs' decisions to stay or leave their school. The findings suggest that schools and districts should consider the degree of likely professional fit between ECTs and their schools when teachers are being hired and take steps to strengthen ECTs' sense of professional fit once they begin teaching.