The focus of this literary study is to examine students’ misconceptions about the equal sign as well as giving upper secondary teacher the tools required to promote students’ understanding of the equal sign. To explore these misconceptions further, the study is framed around three research questions: What misconceptions does students’ have about the equal sign and why do they have them? What consequences do these misconceptions have for students’ mathematical ability? What can you do as a teacher to increase students' understanding of the equal sign and the concept of equality? The study suggests that students mainly struggle with the equal sign due to a unidirectional and dynamic understanding which leads to a series of different problems. This occurs primarily when students work with algebra and equations. Consequently, the study found that teachers have a responsibility to work consistently with the equal sign to counteract these misconceptions. An explicit example of this is that teachers need to bring forth the different meanings that the equal sign pose in different situations. The study also gives a brief history of the equal sign.