Using interview data collected from local teacher-union presidents in ten districts, this study identified the key mechanisms and content of union-sponsored new-teacher socialization efforts. Using a framework of union attachment, the utility of these socialization efforts was evaluated and implications for future research and union-leader practice were offered. Based on the analysis of the findings, the impact of new-teacher socialization on union attachment is often minimal due to the short duration and limited focus of socialization efforts. Therefore calls for sustained socialization within a context of a supportive union culture at the school-level may be warranted.