Ireland's "mathematics problem" is well-documented and extensively reported in the media and elsewhere (Expert Group on Future Skills Needs (EGFSN) 2008; Task Force on the Physical Sciences 2002). Concern primarily lies with post-primary students' underperformance in mathematics coupled with a failure to make a successful transition to third level scientifically and mathematically orientated undergraduate courses. Teacher qualification is believed to be one of the most important factors affecting students' mathematical learning. Research has demonstrated that students learn more from teachers who are skilled, experienced, and know what and how to teach (Darling-Hammond 2000). The aim of this study is to investigate the level of out-of-field teaching occurring in Irish post-primary mathematics classrooms and the deployment of these teachers in Irish second level school. Findings reveal that 48% of teachers teaching mathematics in this study are unqualified to do so and are primarily assigned Junior Cycle classes, non-exam years and Ordinary level or lower mathematics. (Contains 2 figures and 5 tables.)