Acid-base reactions can be described in several ways: by formula equations as reactions between substances, or by ionic equations as proton transfer reactions according to Brønsted‘s model. Both models are introduced in chemistry teaching at Swedish secondary schools. The aim of this study was to determine how textbooks and teachers handle the different models to explain acid-base reactions. First, chemistry textbooks most widely used in Swedish upper secondary schools were examined. Second, semi-structured interviews were conducted with six chemistry teachers. The textbooks neither described the differences between the models used to explain acid-base reactions nor clarified why the Brønsted model was introduced. Teachers were well aware of the importance of using models in their lessons. However, they seemed to have difficulties in applying this view with respect to acids and bases. There was no clear distinction between the models, some teachers had even not reflected on the differences between them. They seemed to rely on the content of chemistry textbooks. Implications for textbook writers, teachers and further research are discussed. [Chem. Educ. Res. Pract., 2005, 6 (1), 19-35]