The efficient use of generalization in textbooks, which are regarded as a supplementary teaching material and constitute a substantial place in the processes of learning and teaching, is important for effective mathematics learning and teaching, as well as for developing mathematical and algebraic thinking. This research seeks to understand how and to what extent middle school mathematics textbooks include both components of generalization in terms of developing algebraic thinking. This study uses the document analysis approach, a qualitative research method, for collecting data. The tasks and exercises in the textbooks have been analyzed using a coding matrix based on the two basic dimensions of the research’s analytical framework. As a result of the research, the tasks and exercises in the textbooks are seen to sufficiently support the component of Generalizing Arithmetic and Quantitative Reasoning, while partially ignoring the component of Patterns and Functional Relationships/Variables. Moreover, the tasks and exercises that are expected to allow students to explore and express generalizations are seen to have been mostly ignored. In addition, generalizations are observed to have been generally associated with everyday life, in parallel with the curriculum.