In this article student teachers’ conceptions of equations are discussed. Data was gathered from 75 student teachers by interviews and questionnaires. Both the quantitative and qualitative research methods were applied in the study. The research results indicate that some specific examples of concepts, which at first appear in teaching, and learning of mathematics are more central to the student teachers than other examples. The former examples are often called prototypes. The investigation shows that students tend to identify the concept equation with one of the prototypical examples and that the concept image develops from one unique prototypical example to include more examples of increasing distance from the prototypical example. The results also indicate that the student teachers’ concept images include erroneous conceptions of the concept equation.