The results of the Teaching and Learning International Survey reflected that teachers’ rate of participation in professional development (PD) activities in the 23 participating countries was 89% on average within the 18 months prior to the survey. However, the participation rate of Turkish teachers in PD activities was 74.8%. In fact, the participation rate of Turkish teachers in PD was the lowest among all participating countries (TALIS, 2009). Thus, the purpose of this study was to examine the relationship between factors (internal [personal] and external [environmental]) and teachers’ participation in PD programs in Turkey. After analyzing the collected data, the researcher found that although age, teachers’ attitudes towards PD activities, time, funding, and colleague influence affect teachers’ participation in PD activities in statistically significant ways; gender, teaching experience, grade level of teaching, education level, teachers’ self-efficacy, principal, and school culture do not affect their participation in these activities in Turkey. The findings of this study inform policy makers regarding methods for increasing teacher participation rates in PD activities.