For more than 30 years, the study of teachers' beliefs has been crucial to the mathematics education field since teachers' beliefs may significantly influence students' learning of mathematics. This study included 127 Estonian in-service primary and secondary school mathematics teachers teaching grades three to five. We examined their beliefs about the nature of mathematics, learning of mathematics, and their confidence in their ability to teach the subject (self-efficacy). Moreover, we aimed to explore the relationships between these beliefs. We also investigated the possible differences between subject teachers and class teachers and possible differences regarding teacher work experience. Teachers' self-efficacy beliefs about goal setting, motivation, and cognitive activation were positively correlated. Self-efficacy beliefs on goal setting had positive effect on rules and procedures beliefs (nature of mathematics) and teacher-directed beliefs (learning of mathematics). In addition, the results showed a negative relationship between self-efficacy beliefs on cognitive activation and rules and procedures and teacher-directed beliefs. No statistically significant relationship was found between the teachers' beliefs and their years of experience. Nonetheless, a strong correlation was discovered between the type of teachers (i.e., class teacher or subject teacher) and self-efficacy beliefs related to cognitive activation. These findings draw attention to the intricate links between teachers' different beliefs and offer recommendations for teacher preparation programs and further study. [Note: The issue number (5) shown on the PDF is incorrect. The correct issue number is 1.]