The professional work as a teacher at schools requires continuing professionalization throughout the whole career. In addition to participation in in-service training and professional development courses, this process also includes the use of informal learning opportunities which exist outside of organized events in everyday professional life, and which are mostly initiated by the teachers themselves. This study focuses on the field of continuing professional development of teachers, which has been little researched so far. Based on a quantitative questionnaire survey of a representative sample of N = 405 teachers from Germany, we applied structural equation models to analyze the factorial structure and the use of informal learning opportunities, as well as their personal and school-related determinants. The findings indicate predictive effects of teachers’ demographic and dispositional characteristics (age, gender, lack of traditional qualification, self-efficacy), but also of job characteristics (extended area of responsibility) on the use of informal learning opportunities. Furthermore, indications pointed to the necessity of differentiating print and online media regarding reception behavior. The role of informal learning opportunities in the context of the teachers’ overall professionalization is discussed.