Numerous studies have shown that pupils and students have difficulties transferring conceptual and procedural mathematical knowledge into the context of physics. Vectors are an important topic in mathematics instruction and are necessary for understanding many physical concepts. In this diploma thesis, understanding of vectors in fourth-grade students of general and science high schools was investigated. Students’ eye movements were measured while they solved a test consisting of 12 isomorphic mathematics and physics items in which the same vector concept was examined. The items examined the following vector concepts: direction and length of vectors, vector components, addition, subtraction, scalar multiplication, and scalar product of vectors. The results showed that students solved mathematics and physics items similarly and often chose the same answer in parallel items. It could be said that the students successfully applied the knowledge of vectors in both contexts, probably because in the physics items the vector concepts to be examined were clearly indicated. Measurement of eye movements provided additional insight into students’ attention as they solved items that examined vector understanding. It turned out that students took longer to solve physics items because the text was longer, and some graphical representations were more complex. The analysis of individual items showed that students had the most difficulties with calculating the scalar product of vectors in the orthonormal base, understanding the geometric interpretation of the scalar product, and subtracting vectors in one and two dimensions. The implications of the obtained results for the teaching of mathematics and physics are discussed.