This theoretical study concerns the issue of representations. Representation is a concept used when analysing and explaining human perception, cognition, communication, and learning. Firstly, we introduce the psychological foundations of the concept. Secondly, we clarify the concept of representations and its division in cognitive psychology. We define two basic forms of external representations – verbal and visual. In social psychology, the concept is used for explaining of how much individual cognition is determined by socio-cultural factors. Further, we mention the concept of representations that draws on the Theory of social representations (Moscovici) and Vygotsky´s ideas. The author seeks to develop a concept of representations usable in didactic discourse. The importance of representations for content-oriented didactics is clarified. We also define the levels on which a teacher reasons when using representations during instruction. Representations of curricular content, which are believed to play an important role when presenting the content to students, are also mentioned.