The aim of this study is to determine the opinions of secondary school mathematics teachers regarding the use of mathematics textbooks. The research was designed in the case study design, which is one of the qualitative research designs. Three mathematics teachers participated in the research. Two of the teachers are female and one is male. While male teachers have 10 years of experience, female teachers have 5 years of experience. In the research, data were collected through semi-structured interviews, observation and document review. Content analysis method was used to analyze the research data. The research findings are collected under the headings of the purposes of use of textbooks, the use of textbooks, the advantages and disadvantages of textbooks, the difficulties encountered in the use of textbooks, and the features of effective and useful mathematics textbooks. As a result of the research, it was determined that teachers generally used textbooks for the purpose of controlling the order of achievements, controlling the activity steps and assigning homework as a result of the course process. Teachers generally use the textbook in the introductory activities of their courses and in solving sample questions. Teachers stated that among the disadvantages of textbooks are the fact that they contain a small number of questions related to the textbooks, there is unnecessary complexity in some subjects, and they are not compatible with central exams. Teachers stated that the difficulties they experienced with the textbook were the topics that were not suitable for the student level and the wrong order of the topics. Teachers defined a good quality mathematics book as one that is supported by technology, contains questions compatible with central exams, contains plenty of questions and solutions, and includes fun activities.