This article attempts to define the role and function of sensitisation, also known as a "linguistic warm-up" in a foreign language lesson. Using arguments embedded in the constructivist paradigm, it is shown that the linguistic warm-up is an indispensable element of an effective didactic process, performing primarily a motivating and autonomising function. The article mainly demonstrates the role of the warm-up in activating the previous knowledge of a student and emphasises its importance for the possibility of supporting the "bottom-up" processes in the course of the lesson. The warm-up is also assigned the function of activating anchoring ideas by referring to Ausubel's theory of advance organisers and his concept of meaningful learning. In addition, the article describes how the linguistic warm-up is interpreted in the German language curricula, and briefly presents the author's point of view on the issue of sensitisation in the process of foreign language education.