The purpose of this study is to analyse what kind of conceptions secondaryteachers in mathematics have of the equation concept and what kind of experiencesgave rise to their own concept learning. Ten secondary school teachers ofmathematics participated in the study. Data was gathered by interviews andquestionnaires. The ‘phenomenographic’ research method was applied ininterpreting the results of the investigation. The results indicate that the teachers’conceptions of the equation concept differ from the formal definition of the equationconcept. At school they spent most of their time developing procedural skills insteadof mathematical understanding.