Concerns about teacher attrition and associated teacher shortages are widespread. This multilevel study explores the relative importance of three main mechanisms through the investigation of relevant teacher, school, and country characteristics: (A) selection mechanisms related to who becomes a teacher; (B) early career support resources related to entering the profession; and (C) long-term support resources related to developing a teaching career. Using the 2018 Teaching And Learning International Survey (TALIS), retention intention is analysed using information from 11 613 early-career teachers in 3998 schools in 31 countries. Results underline the importance of selection processes at individual and country level.