Аннотация:Beyond elementary levels, little has been researched about the mathematical beliefs -beliefs about mathematics, their teaching and their learning-of in-service teachers.To begin filling this gap, the present qualitative research aims to identify, without imposing categories, the mathematical beliefs that 18 Mexican high school teachers have.For the analysis of the data, collected through semi-structured interviews, we conducted three thematic analysis guided by the definition that a belief is what an individual considers true.The results indicate that 'mathematics is to be applied / used' and that 'mathematics is to reason', 'to solve problems' and 'to make decisions' are the main beliefs about the mathematics from which the Learning beliefs of mathematics and the main beliefs about the teaching of mathematics.The existence of the identified beliefs can be explained in two complementary ways: by the daily context of the participants and by their condition as teachers with professional training of engineers.
