In this study we analyse conceptions that prospective teachers in mathematics have about equations and how these conceptions are related to the truth value (of mathematical statements). Our phenomenographic research reveals that there exists a large variety of fundamentally different conceptions about equations and that in students’ actual concept image of equation it is commonly assumed that a mathematical expression must possess the truth value ‘true’ in order to be an equation in spite of the fact that any consideration related to the truth value only rarely appears in concept definitions given by students.