This study aims to document and examine mathematics teacher educators' (MTEs) knowledge sources in teacher education practices. The study adopts a mixed-method, embedded research design. Data were collected via a questionnaire with elicitations about MTEs' descriptive features as well as with open-ended items. Target population was all MTEs working in mathematics education departments across Turkish universities. The questionnaire was emailed to all MTEs, and 281 out of 522 returned with their answers. MTEs' written statements were examined via inductive thematic analysis. A post hoc quantitative analysis was also conducted to explore the relationships between knowledge sources and four variables: gender, self-identification, teaching experience and academic ranking. The analysis allowed the determination of a variety of knowledge sources in teacher education practices and established certain relationships. The findings are discussed with regard to MTEs' professional development, conceptions of knowing and learning and the contribution of different sources to the teacher education practices.